git-multimail: an improved replacement for post-receive-email

Add git-multimail, a tool for generating notification emails for
pushes to a Git repository.  It is largely plug-in compatible with
post-receive-email, and is proposed to eventually replace that script.
The advantages of git-multimail relative to post-receive-email are
described in README.migrate-from-post-receive-email.

git-multimail is organized in a directory contrib/hooks/multimail.
The directory contains:

* git_multimail.py -- a Python module that can generate notification
  emails for pushes to a Git repository.  The file can be used
  directly as a post-receive script (configured via git config
  settings), or it can be imported as a Python module and configured
  via arbitrary Python code.

* README -- user-level documentation for configuring and using
  git-multimail.

* post-receive -- an example of building a post-receive script that
  imports git_multimail.py as a Python module, with an example of how
  to change the email templates.

* README.migrate-from-post-receive-email -- documentation targeted at
  current users of post-receive-email, explaining the differences and
  how to migrate a post-receive-email configuration to git-multimail.

* migrate-mailhook-config -- a script that can migrate a user's
  post-receive-email configuration options to the equivalent
  git-multimail options.

* README.Git -- a short explanation of the relationship between
  git-multimail and the rest of the Git project, plus the exact date
  and revision when this version was taken from the upstream project.

All but the last file are taken verbatim from the upstream
git-multimail project.

git-multimail is originally derived from post-receive-email and also
incorporates suggestions from the mailing list as well as patches by
the people listed below.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Contributions-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Contributions-by: Ramkumar Ramachandra <artagnon@gmail.com>
Contributions-by: Chris Hiestand <chrishiestand@gmail.com>
Contributions-by: Michiel Holtkamp <git@elfstone.nl>
Contributions-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 3398 insertions, 0 deletions

diff --git a/contrib/hooks/multimail/README b/contrib/hooks/multimail/README
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+			   git-multimail
+			   =============
+
+git-multimail is a tool for sending notification emails on pushes to a
+Git repository.  It includes a Python module called git_multimail.py,
+which can either be used as a hook script directly or can be imported
+as a Python module into another script.
+
+git-multimail is derived from the Git project's old
+contrib/hooks/post-receive-email, and is mostly compatible with that
+script.  See README.migrate-from-post-receive-email for details about
+the differences and for how to migrate from post-receive-email to
+git-multimail.
+
+git-multimail, like the rest of the Git project, is licensed under
+GPLv2 (see the COPYING file for details).
+
+Please note: although, as a convenience, git-multimail may be
+distributed along with the main Git project, development of
+git-multimail takes place in its own, separate project.  See section
+"Getting involved" below for more information.
+
+
+By default, for each push received by the repository, git-multimail:
+
+1. Outputs one email summarizing each reference that was changed.
+   These "reference change" (called "refchange" below) emails describe
+   the nature of the change (e.g., was the reference created, deleted,
+   fast-forwarded, etc.) and include a one-line summary of each commit
+   that was added to the reference.
+
+2. Outputs one email for each new commit that was introduced by the
+   reference change.  These "commit" emails include a list of the
+   files changed by the commit, followed by the diffs of files
+   modified by the commit.  The commit emails are threaded to the
+   corresponding reference change email via "In-Reply-To".  This style
+   (similar to the "git format-patch" style used on the Git mailing
+   list) makes it easy to scan through the emails, jump to patches
+   that need further attention, and write comments about specific
+   commits.  Commits are handled in reverse topological order (i.e.,
+   parents shown before children).  For example,
+
+   [git] branch master updated
+   + [git] 01/08: doc: fix xref link from api docs to manual pages
+   + [git] 02/08: api-credentials.txt: show the big picture first
+   + [git] 03/08: api-credentials.txt: mention credential.helper explicitly
+   + [git] 04/08: api-credentials.txt: add "see also" section
+   + [git] 05/08: t3510 (cherry-pick-sequence): add missing '&&'
+   + [git] 06/08: Merge branch 'rr/maint-t3510-cascade-fix'
+   + [git] 07/08: Merge branch 'mm/api-credentials-doc'
+   + [git] 08/08: Git 1.7.11-rc2
+
+   Each commit appears in exactly one commit email, the first time
+   that it is pushed to the repository.  If a commit is later merged
+   into another branch, then a one-line summary of the commit is
+   included in the reference change email (as usual), but no
+   additional commit email is generated.
+
+   By default, reference change emails have their "Reply-To" field set
+   to the person who pushed the change, and commit emails have their
+   "Reply-To" field set to the author of the commit.
+
+3. Output one "announce" mail for each new annotated tag, including
+   information about the tag and optionally a shortlog describing the
+   changes since the previous tag.  Such emails might be useful if you
+   use annotated tags to mark releases of your project.
+
+
+Requirements
+------------
+
+* Python 2.x, version 2.4 or later.  No non-standard Python modules
+  are required.  git-multimail does *not* currently work with Python
+  3.x.
+
+  The example scripts invoke Python using the following shebang line
+  (following PEP 394 [1]):
+
+      #! /usr/bin/env python2
+
+  If your system's Python2 interpreter is not in your PATH or is not
+  called "python2", you can change the lines accordingly.  Or you can
+  invoke the Python interpreter explicitly, for example via a tiny
+  shell script like
+
+      #! /bin/sh
+      /usr/local/bin/python /path/to/git_multimail.py "$@"
+
+* The "git" command must be in your PATH.  git-multimail is known to
+  work with Git versions back to 1.7.1.  (Earlier versions have not
+  been tested; if you do so, please report your results.)
+
+* To send emails using the default configuration, a standard sendmail
+  program must be located at '/usr/sbin/sendmail' and configured
+  correctly to send emails.  If this is not the case, see the
+  multimailhook.mailer configuration variable below for how to
+  configure git-multimail to send emails via an SMTP server.
+
+
+Invocation
+----------
+
+git_multimail.py is designed to be used as a "post-receive" hook in a
+Git repository (see githooks(5)).  Link or copy it to
+$GIT_DIR/hooks/post-receive within the repository for which email
+notifications are desired.  Usually it should be installed on the
+central repository for a project, to which all commits are eventually
+pushed.
+
+For use on pre-v1.5.1 Git servers, git_multimail.py can also work as
+an "update" hook, taking its arguments on the command line.  To use
+this script in this manner, link or copy it to $GIT_DIR/hooks/update.
+Please note that the script is not completely reliable in this mode
+[2].
+
+Alternatively, git_multimail.py can be imported as a Python module
+into your own Python post-receive script.  This method is a bit more
+work, but allows the behavior of the hook to be customized using
+arbitrary Python code.  For example, you can use a custom environment
+(perhaps inheriting from GenericEnvironment or GitoliteEnvironment) to
+
+* change how the user who did the push is determined
+
+* read users' email addresses from an LDAP server or from a database
+
+* decide which users should be notified about which commits based on
+  the contents of the commits (e.g., for users who want to be notified
+  only about changes affecting particular files or subdirectories)
+
+Or you can change how emails are sent by writing your own Mailer
+class.  The "post-receive" script in this directory demonstrates how
+to use git_multimail.py as a Python module.  (If you make interesting
+changes of this type, please consider sharing them with the
+community.)
+
+
+Configuration
+-------------
+
+By default, git-multimail mostly takes its configuration from the
+following "git config" settings:
+
+multimailhook.environment
+
+    This describes the general environment of the repository.
+    Currently supported values:
+
+    "generic" -- the username of the pusher is read from $USER and the
+        repository name is derived from the repository's path.
+
+    "gitolite" -- the username of the pusher is read from $GL_USER and
+        the repository name from $GL_REPO.
+
+    If neither of these environments is suitable for your setup, then
+    you can implement a Python class that inherits from Environment
+    and instantiate it via a script that looks like the example
+    post-receive script.
+
+    The environment value can be specified on the command line using
+    the --environment option.  If it is not specified on the command
+    line or by multimailhook.environment, then it defaults to
+    "gitolite" if the environment contains variables $GL_USER and
+    $GL_REPO; otherwise "generic".
+
+multimailhook.repoName
+
+    A short name of this Git repository, to be used in various places
+    in the notification email text.  The default is to use $GL_REPO
+    for gitolite repositories, or otherwise to derive this value from
+    the repository path name.
+
+multimailhook.mailinglist
+
+    The list of email addresses to which notification emails should be
+    sent, as RFC 2822 email addresses separated by commas.  This
+    configuration option can be multivalued.  Leave it unset or set it
+    to the empty string to not send emails by default.  The next few
+    settings can be used to configure specific address lists for
+    specific types of notification email.
+
+multimailhook.refchangeList
+
+    The list of email addresses to which summary emails about
+    reference changes should be sent, as RFC 2822 email addresses
+    separated by commas.  This configuration option can be
+    multivalued.  The default is the value in
+    multimailhook.mailinglist.  Set this value to the empty string to
+    prevent reference change emails from being sent.
+
+multimailhook.announceList
+
+    The list of email addresses to which emails about new annotated
+    tags should be sent, as RFC 2822 email addresses separated by
+    commas.  This configuration option can be multivalued.  The
+    default is the value in multimailhook.refchangelist or
+    multimailhook.mailinglist.  Set this value to the empty string to
+    prevent annotated tag announcement emails from being sent.
+
+multimailhook.commitList
+
+    The list of email addresses to which emails about individual new
+    commits should be sent, as RFC 2822 email addresses separated by
+    commas.  This configuration option can be multivalued.  The
+    default is the value in multimailhook.mailinglist.  Set this value
+    to the empty string to prevent notification emails about
+    individual commits from being sent.
+
+multimailhook.announceShortlog
+
+    If this option is set to true, then emails about changes to
+    annotated tags include a shortlog of changes since the previous
+    tag.  This can be useful if the annotated tags represent releases;
+    then the shortlog will be a kind of rough summary of what has
+    happened since the last release.  But if your tagging policy is
+    not so straightforward, then the shortlog might be confusing
+    rather than useful.  Default is false.
+
+multimailhook.refchangeShowLog
+
+    If this option is set to true, then summary emails about reference
+    changes will include a detailed log of the added commits in
+    addition to the one line summary.  The log is generated by running
+    "git log" with the options specified in multimailhook.logOpts.
+    Default is false.
+
+multimailhook.mailer
+
+    This option changes the way emails are sent.  Accepted values are:
+
+    - sendmail (the default): use the command /usr/sbin/sendmail or
+      /usr/lib/sendmail (or sendmailCommand, if configured).  This
+      mode can be further customized via the following options:
+
+       multimailhook.sendmailCommand
+
+           The command used by mailer "sendmail" to send emails.  Shell
+           quoting is allowed in the value of this setting, but remember that
+           Git requires double-quotes to be escaped; e.g.,
+
+             git config multimailhook.sendmailcommand '/usr/sbin/sendmail -t -F \"Git Repo\"'
+
+           Default is '/usr/sbin/sendmail -t' or '/usr/lib/sendmail
+           -t' (depending on which file is present and executable).
+
+       multimailhook.envelopeSender
+
+           If set then pass this value to sendmail via the -f option to set
+           the envelope sender address.
+
+    - smtp: use Python's smtplib.  This is useful when the sendmail
+      command is not available on the system.  This mode can be
+      further customized via the following options:
+
+       multimailhook.smtpServer
+
+           The name of the SMTP server to connect to.  The value can
+           also include a colon and a port number; e.g.,
+           "mail.example.com:25".  Default is 'localhost' using port
+           25.
+
+       multimailhook.envelopeSender
+
+           The sender address to be passed to the SMTP server.  If
+           unset, then the value of multimailhook.from is used.
+
+multimailhook.from
+
+    If set then use this value in the From: field of generated emails.
+    If unset, then use the repository's user configuration (user.name
+    and user.email).  If user.email is also unset, then use
+    multimailhook.envelopeSender.
+
+multimailhook.administrator
+
+    The name and/or email address of the administrator of the Git
+    repository; used in FOOTER_TEMPLATE.  Default is
+    multimailhook.envelopesender if it is set; otherwise a generic
+    string is used.
+
+multimailhook.emailPrefix
+
+    All emails have this string prepended to their subjects, to aid
+    email filtering (though filtering based on the X-Git-* email
+    headers is probably more robust).  Default is the short name of
+    the repository in square brackets; e.g., "[myrepo]".
+
+multimailhook.emailMaxLines
+
+    The maximum number of lines that should be included in the body of
+    a generated email.  If not specified, there is no limit.  Lines
+    beyond the limit are suppressed and counted, and a final line is
+    added indicating the number of suppressed lines.
+
+multimailhook.emailMaxLineLength
+
+    The maximum length of a line in the email body.  Lines longer than
+    this limit are truncated to this length with a trailing " [...]"
+    added to indicate the missing text.  The default is 500, because
+    (a) diffs with longer lines are probably from binary files, for
+    which a diff is useless, and (b) even if a text file has such long
+    lines, the diffs are probably unreadable anyway.  To disable line
+    truncation, set this option to 0.
+
+multimailhook.maxCommitEmails
+
+    The maximum number of commit emails to send for a given change.
+    When the number of patches is larger that this value, only the
+    summary refchange email is sent.  This can avoid accidental
+    mailbombing, for example on an initial push.  To disable commit
+    emails limit, set this option to 0.  The default is 500.
+
+multimailhook.emailStrictUTF8
+
+    If this boolean option is set to "true", then the main part of the
+    email body is forced to be valid UTF-8.  Any characters that are
+    not valid UTF-8 are converted to the Unicode replacement
+    character, U+FFFD.  The default is "true".
+
+multimailhook.diffOpts
+
+    Options passed to "git diff-tree" when generating the summary
+    information for ReferenceChange emails.  Default is "--stat
+    --summary --find-copies-harder".  Add -p to those options to
+    include a unified diff of changes in addition to the usual summary
+    output.  Shell quoting is allowed; see multimailhook.logOpts for
+    details.
+
+multimailhook.logOpts
+
+    Options passed to "git log" to generate additional info for
+    reference change emails (used only if refchangeShowLog is set).
+    For example, adding --graph will show the graph of revisions, -p
+    will show the complete diff, etc.  The default is empty.
+
+    Shell quoting is allowed; for example, a log format that contains
+    spaces can be specified using something like:
+
+      git config multimailhook.logopts '--pretty=format:"%h %aN <%aE>%n%s%n%n%b%n"'
+
+    If you want to set this by editing your configuration file
+    directly, remember that Git requires double-quotes to be escaped
+    (see git-config(1) for more information):
+
+      [multimailhook]
+              logopts = --pretty=format:\"%h %aN <%aE>%n%s%n%n%b%n\"
+
+multimailhook.emailDomain
+
+    Domain name appended to the username of the person doing the push
+    to convert it into an email address (via "%s@%s" % (username,
+    emaildomain)).  More complicated schemes can be implemented by
+    overriding Environment and overriding its get_pusher_email()
+    method.
+
+multimailhook.replyTo
+multimailhook.replyToCommit
+multimailhook.replyToRefchange
+
+    Addresses to use in the Reply-To: field for commit emails
+    (replyToCommit) and refchange emails (replyToRefchange).
+    multimailhook.replyTo is used as default when replyToCommit or
+    replyToRefchange is not set.  The value for these variables can be
+    either:
+
+    - An email address, which will be used directly.
+
+    - The value "pusher", in which case the pusher's address (if
+      available) will be used.  This is the default for refchange
+      emails.
+
+    - The value "author" (meaningful only for replyToCommit), in which
+      case the commit author's address will be used.  This is the
+      default for commit emails.
+
+    - The value "none", in which case the Reply-To: field will be
+      omitted.
+
+
+Email filtering aids
+--------------------
+
+All emails include extra headers to enable fine tuned filtering and
+give information for debugging.  All emails include the headers
+"X-Git-Repo", "X-Git-Refname", and "X-Git-Reftype".  ReferenceChange
+emails also include headers "X-Git-Oldrev" and "X-Git-Newrev";
+Revision emails also include header "X-Git-Rev".
+
+
+Customizing email contents
+--------------------------
+
+git-multimail mostly generates emails by expanding templates.  The
+templates can be customized.  To avoid the need to edit
+git_multimail.py directly, the preferred way to change the templates
+is to write a separate Python script that imports git_multimail.py as
+a module, then replaces the templates in place.  See the provided
+post-receive script for an example of how this is done.
+
+
+Customizing git-multimail for your environment
+----------------------------------------------
+
+git-multimail is mostly customized via an "environment" that describes
+the local environment in which Git is running.  Two types of
+environment are built in:
+
+* GenericEnvironment: a stand-alone Git repository.
+
+* GitoliteEnvironment: a Git repository that is managed by gitolite
+  [3].  For such repositories, the identity of the pusher is read from
+  environment variable $GL_USER, and the name of the repository is
+  read from $GL_REPO (if it is not overridden by
+  multimailhook.reponame).
+
+By default, git-multimail assumes GitoliteEnvironment if $GL_USER and
+$GL_REPO are set, and otherwise assumes GenericEnvironment.
+Alternatively, you can choose one of these two environments explicitly
+by setting a "multimailhook.environment" config setting (which can
+have the value "generic" or "gitolite") or by passing an --environment
+option to the script.
+
+If you need to customize the script in ways that are not supported by
+the existing environments, you can define your own environment class
+class using arbitrary Python code.  To do so, you need to import
+git_multimail.py as a Python module, as demonstrated by the example
+post-receive script.  Then implement your environment class; it should
+usually inherit from one of the existing Environment classes and
+possibly one or more of the EnvironmentMixin classes.  Then set the
+"environment" variable to an instance of your own environment class
+and pass it to run_as_post_receive_hook().
+
+The standard environment classes, GenericEnvironment and
+GitoliteEnvironment, are in fact themselves put together out of a
+number of mixin classes, each of which handles one aspect of the
+customization.  For the finest control over your configuration, you
+can specify exactly which mixin classes your own environment class
+should inherit from, and override individual methods (or even add your
+own mixin classes) to implement entirely new behaviors.  If you
+implement any mixins that might be useful to other people, please
+consider sharing them with the community!
+
+
+Getting involved
+----------------
+
+git-multimail is an open-source project, built by volunteers.  We
+would welcome your help!
+
+The current maintainer is Michael Haggerty <mhagger@alum.mit.edu>.
+
+General discussion of git-multimail takes place on the main Git
+mailing list,
+
+    git@vger.kernel.org
+
+Please CC emails regarding git-multimail to me so that I don't
+overlook them.
+
+The git-multimail project itself is currently hosted on GitHub:
+
+    https://github.com/mhagger/git-multimail
+
+We use the GitHub issue tracker to keep track of bugs and feature
+requests, and GitHub pull requests to exchange patches (though, if you
+prefer, you can send patches via the Git mailing list with cc to me).
+
+Please note that although a copy of git-multimail will probably be
+distributed in the "contrib" section of the main Git project,
+development takes place in the separate git-multimail repository on
+GitHub!  (Whenever enough changes to git-multimail have accumulated, a
+new code-drop of git-multimail will be submitted for inclusion in the
+Git project.)
+
+
+Footnotes
+---------
+
+[1] http://www.python.org/dev/peps/pep-0394/
+
+[2] Because of the way information is passed to update hooks, the
+    script's method of determining whether a commit has already been
+    seen does not work when it is used as an "update" script.  In
+    particular, no notification email will be generated for a new
+    commit that is added to multiple references in the same push.
+
+[3] https://github.com/sitaramc/gitolite
diff --git a/contrib/hooks/multimail/README.Git b/contrib/hooks/multimail/README.Git
new file mode 100644
index 0000000000..9c2e66a69a
--- /dev/null
+++ b/contrib/hooks/multimail/README.Git
@@ -0,0 +1,15 @@
+This copy of git-multimail is distributed as part of the "contrib"
+section of the Git project as a convenience to Git users.
+git-multimail is developed as an independent project at the following
+website:
+
+    https://github.com/mhagger/git-multimail
+
+The version in this directory was obtained from the upstream project
+on 2013-07-14 and consists of the "git-multimail" subdirectory from
+revision
+
+    1a5cb09c698a74d15a715a86b09ead5f56bf4b06
+
+Please see the README file in this directory for information about how
+to report bugs or contribute to git-multimail.
diff --git a/contrib/hooks/multimail/README.migrate-from-post-receive-email b/contrib/hooks/multimail/README.migrate-from-post-receive-email
new file mode 100644
index 0000000000..1e6a976699
--- /dev/null
+++ b/contrib/hooks/multimail/README.migrate-from-post-receive-email
@@ -0,0 +1,145 @@
+git-multimail is close to, but not exactly, a plug-in replacement for
+the old Git project script contrib/hooks/post-receive-email.  This
+document describes the differences and explains how to configure
+git-multimail to get behavior closest to that of post-receive-email.
+
+If you are in a hurry
+=====================
+
+A script called migrate-mailhook-config is included with
+git-multimail.  If you run this script within a Git repository that is
+configured to use post-receive-email, it will convert the
+configuration settings into the approximate equivalent settings for
+git-multimail.  For more information, run
+
+    migrate-mailhook-config --help
+
+
+Configuration differences
+=========================
+
+* The names of the config options for git-multimail are in namespace
+  "multimailhook.*" instead of "hooks.*".  (Editorial comment:
+  post-receive-email should never have used such a generic top-level
+  namespace.)
+
+* In emails about new annotated tags, post-receive-email includes a
+  shortlog of all changes since the previous annotated tag.  To get
+  this behavior with git-multimail, you need to set
+  multimailhook.announceshortlog to true:
+
+      git config multimailhook.announceshortlog true
+
+* multimailhook.commitlist -- This is a new configuration variable.
+  Recipients listed here will receive a separate email for each new
+  commit.  However, if this variable is *not* set, it defaults to the
+  value of multimailhook.mailinglist.  Therefore, if you *don't* want
+  the members of multimailhook.mailinglist to receive one email per
+  commit, then set this value to the empty string:
+
+      git config multimailhook.commitlist ''
+
+* multimailhook.emailprefix -- If this value is not set, then the
+  subjects of generated emails are prefixed with the short name of the
+  repository enclosed in square brackets; e.g., "[myrepo]".
+  post-receive-email defaults to prefix "[SCM]" if this option is not
+  set.  So if you were using the old default and want to retain it
+  (for example, to avoid having to change your email filters), set
+  this variable explicitly to the old value:
+
+      git config multimailhook.emailprefix "[SCM]"
+
+* The "multimailhook.showrev" configuration option is not supported.
+  Its main use is obsoleted by the one-email-per-commit feature of
+  git-multimail.
+
+
+Other differences
+=================
+
+This section describes other differences in the behavior of
+git-multimail vs. post-receive-email.  For full details, please refer
+to the main README file:
+
+* One email per commit.  For each reference change, the script first
+  outputs one email summarizing the reference change (including
+  one-line summaries of the new commits), then it outputs a separate
+  email for each new commit that was introduced, including patches.
+  These one-email-per-commit emails go to the addresses listed in
+  multimailhook.commitlist.  post-receive-email sends only one email
+  for each *reference* that is changed, no matter how many commits
+  were added to the reference.
+
+* Better algorithm for detecting new commits.  post-receive-email
+  processes one reference change at a time, which causes it to fail to
+  describe new commits that were included in multiple branches.  For
+  example, if a single push adds the "*" commits in the diagram below,
+  then post-receive-email would never include the details of the two
+  commits that are common to "master" and "branch" in its
+  notifications.
+
+      o---o---o---*---*---*    <-- master
+                       \
+                        *---*  <-- branch
+
+  git-multimail analyzes all reference modifications to determine
+  which commits were not present before the change, therefore avoiding
+  that error.
+
+* In reference change emails, git-multimail tells which commits have
+  been added to the reference vs. are entirely new to the repository,
+  and which commits that have been omitted from the reference
+  vs. entirely discarded from the repository.
+
+* The environment in which Git is running can be configured via an
+  "Environment" abstraction.
+
+* Built-in support for Gitolite-managed repositories.
+
+* Instead of using full SHA1 object names in emails, git-multimail
+  mostly uses abbreviated SHA1s, plus one-line log message summaries
+  where appropriate.
+
+* In the schematic diagrams that explain non-fast-forward commits,
+  git-multimail shows the names of the branches involved.
+
+* The emails generated by git-multimail include the name of the Git
+  repository that was modified; this is convenient for recipients who
+  are monitoring multiple repositories.
+
+* git-multimail allows the email "From" addresses to be configured.
+
+* The recipients lists (multimailhook.mailinglist,
+  multimailhook.refchangelist, multimailhook.announcelist, and
+  multimailhook.commitlist) can be comma-separated values and/or
+  multivalued settings in the config file; e.g.,
+
+      [multimailhook]
+              mailinglist = mr.brown@example.com, mr.black@example.com
+              announcelist = Him <him@example.com>
+              announcelist = Jim <jim@example.com>
+              announcelist = pop@example.com
+
+  This might make it easier to maintain short recipients lists without
+  requiring full-fledged mailing list software.
+
+* By default, git-multimail sets email "Reply-To" headers to reply to
+  the pusher (for reference updates) and to the author (for commit
+  notifications).  By default, the pusher's email address is
+  constructed by appending "multimailhook.emaildomain" to the pusher's
+  username.
+
+* The generated emails contain a configurable footer.  By default, it
+  lists the name of the administrator who should be contacted to
+  unsubscribe from notification emails.
+
+* New option multimailhook.emailmaxlinelength to limit the length of
+  lines in the main part of the email body.  The default limit is 500
+  characters.
+
+* New option multimailhook.emailstrictutf8 to ensure that the main
+  part of the email body is valid UTF-8.  Invalid characters are
+  turned into the Unicode replacement character, U+FFFD.  By default
+  this option is turned on.
+
+* Written in Python.  Easier to add new features.
diff --git a/contrib/hooks/multimail/git_multimail.py b/contrib/hooks/multimail/git_multimail.py
new file mode 100755
index 0000000000..81c6a51706
--- /dev/null
+++ b/contrib/hooks/multimail/git_multimail.py
@@ -0,0 +1,2393 @@
+#! /usr/bin/env python2
+
+# Copyright (c) 2012,2013 Michael Haggerty
+# Derived from contrib/hooks/post-receive-email, which is
+# Copyright (c) 2007 Andy Parkins
+# and also includes contributions by other authors.
+#
+# This file is part of git-multimail.
+#
+# git-multimail is free software: you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version
+# 2 as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see
+# <http://www.gnu.org/licenses/>.
+
+"""Generate notification emails for pushes to a git repository.
+
+This hook sends emails describing changes introduced by pushes to a
+git repository.  For each reference that was changed, it emits one
+ReferenceChange email summarizing how the reference was changed,
+followed by one Revision email for each new commit that was introduced
+by the reference change.
+
+Each commit is announced in exactly one Revision email.  If the same
+commit is merged into another branch in the same or a later push, then
+the ReferenceChange email will list the commit's SHA1 and its one-line
+summary, but no new Revision email will be generated.
+
+This script is designed to be used as a "post-receive" hook in a git
+repository (see githooks(5)).  It can also be used as an "update"
+script, but this usage is not completely reliable and is deprecated.
+
+To help with debugging, this script accepts a --stdout option, which
+causes the emails to be written to standard output rather than sent
+using sendmail.
+
+See the accompanying README file for the complete documentation.
+
+"""
+
+import sys
+import os
+import re
+import bisect
+import subprocess
+import shlex
+import optparse
+import smtplib
+
+try:
+    from email.utils import make_msgid
+    from email.utils import getaddresses
+    from email.utils import formataddr
+    from email.header import Header
+except ImportError:
+    # Prior to Python 2.5, the email module used different names:
+    from email.Utils import make_msgid
+    from email.Utils import getaddresses
+    from email.Utils import formataddr
+    from email.Header import Header
+
+
+DEBUG = False
+
+ZEROS = '0' * 40
+LOGBEGIN = '- Log -----------------------------------------------------------------\n'
+LOGEND = '-----------------------------------------------------------------------\n'
+
+
+# It is assumed in many places that the encoding is uniformly UTF-8,
+# so changing these constants is unsupported.  But define them here
+# anyway, to make it easier to find (at least most of) the places
+# where the encoding is important.
+(ENCODING, CHARSET) = ('UTF-8', 'utf-8')
+
+
+REF_CREATED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s created'
+    ' (now %(newrev_short)s)'
+    )
+REF_UPDATED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s updated'
+    ' (%(oldrev_short)s -> %(newrev_short)s)'
+    )
+REF_DELETED_SUBJECT_TEMPLATE = (
+    '%(emailprefix)s%(refname_type)s %(short_refname)s deleted'
+    ' (was %(oldrev_short)s)'
+    )
+
+REFCHANGE_HEADER_TEMPLATE = """\
+To: %(recipients)s
+Subject: %(subject)s
+MIME-Version: 1.0
+Content-Type: text/plain; charset=%(charset)s
+Content-Transfer-Encoding: 8bit
+Message-ID: %(msgid)s
+From: %(fromaddr)s
+Reply-To: %(reply_to)s
+X-Git-Repo: %(repo_shortname)s
+X-Git-Refname: %(refname)s
+X-Git-Reftype: %(refname_type)s
+X-Git-Oldrev: %(oldrev)s
+X-Git-Newrev: %(newrev)s
+Auto-Submitted: auto-generated
+"""
+
+REFCHANGE_INTRO_TEMPLATE = """\
+This is an automated email from the git hooks/post-receive script.
+
+%(pusher)s pushed a change to %(refname_type)s %(short_refname)s
+in repository %(repo_shortname)s.
+
+"""
+
+
+FOOTER_TEMPLATE = """\
+
+-- \n\
+To stop receiving notification emails like this one, please contact
+%(administrator)s.
+"""
+
+
+REWIND_ONLY_TEMPLATE = """\
+This update removed existing revisions from the reference, leaving the
+reference pointing at a previous point in the repository history.
+
+ * -- * -- N   %(refname)s (%(newrev_short)s)
+            \\
+             O -- O -- O   (%(oldrev_short)s)
+
+Any revisions marked "omits" are not gone; other references still
+refer to them.  Any revisions marked "discards" are gone forever.
+"""
+
+
+NON_FF_TEMPLATE = """\
+This update added new revisions after undoing existing revisions.
+That is to say, some revisions that were in the old version of the
+%(refname_type)s are not in the new version.  This situation occurs
+when a user --force pushes a change and generates a repository
+containing something like this:
+
+ * -- * -- B -- O -- O -- O   (%(oldrev_short)s)
+            \\
+             N -- N -- N   %(refname)s (%(newrev_short)s)
+
+You should already have received notification emails for all of the O
+revisions, and so the following emails describe only the N revisions
+from the common base, B.
+
+Any revisions marked "omits" are not gone; other references still
+refer to them.  Any revisions marked "discards" are gone forever.
+"""
+
+
+NO_NEW_REVISIONS_TEMPLATE = """\
+No new revisions were added by this update.
+"""
+
+
+DISCARDED_REVISIONS_TEMPLATE = """\
+This change permanently discards the following revisions:
+"""
+
+
+NO_DISCARDED_REVISIONS_TEMPLATE = """\
+The revisions that were on this %(refname_type)s are still contained in
+other references; therefore, this change does not discard any commits
+from the repository.
+"""
+
+
+NEW_REVISIONS_TEMPLATE = """\
+The %(tot)s revisions listed above as "new" are entirely new to this
+repository and will be described in separate emails.  The revisions
+listed as "adds" were already present in the repository and have only
+been added to this reference.
+
+"""
+
+
+TAG_CREATED_TEMPLATE = """\
+        at  %(newrev_short)-9s (%(newrev_type)s)
+"""
+
+
+TAG_UPDATED_TEMPLATE = """\
+*** WARNING: tag %(short_refname)s was modified! ***
+
+      from  %(oldrev_short)-9s (%(oldrev_type)s)
+        to  %(newrev_short)-9s (%(newrev_type)s)
+"""
+
+
+TAG_DELETED_TEMPLATE = """\
+*** WARNING: tag %(short_refname)s was deleted! ***
+
+"""
+
+
+# The template used in summary tables.  It looks best if this uses the
+# same alignment as TAG_CREATED_TEMPLATE and TAG_UPDATED_TEMPLATE.
+BRIEF_SUMMARY_TEMPLATE = """\
+%(action)10s  %(rev_short)-9s %(text)s
+"""
+
+
+NON_COMMIT_UPDATE_TEMPLATE = """\
+This is an unusual reference change because the reference did not
+refer to a commit either before or after the change.  We do not know
+how to provide full information about this reference change.
+"""
+
+
+REVISION_HEADER_TEMPLATE = """\
+To: %(recipients)s
+Subject: %(emailprefix)s%(num)02d/%(tot)02d: %(oneline)s
+MIME-Version: 1.0
+Content-Type: text/plain; charset=%(charset)s
+Content-Transfer-Encoding: 8bit
+From: %(fromaddr)s
+Reply-To: %(reply_to)s
+In-Reply-To: %(reply_to_msgid)s
+References: %(reply_to_msgid)s
+X-Git-Repo: %(repo_shortname)s
+X-Git-Refname: %(refname)s
+X-Git-Reftype: %(refname_type)s
+X-Git-Rev: %(rev)s
+Auto-Submitted: auto-generated
+"""
+
+REVISION_INTRO_TEMPLATE = """\
+This is an automated email from the git hooks/post-receive script.
+
+%(pusher)s pushed a commit to %(refname_type)s %(short_refname)s
+in repository %(repo_shortname)s.
+
+"""
+
+
+REVISION_FOOTER_TEMPLATE = FOOTER_TEMPLATE
+
+
+class CommandError(Exception):
+    def __init__(self, cmd, retcode):
+        self.cmd = cmd
+        self.retcode = retcode
+        Exception.__init__(
+            self,
+            'Command "%s" failed with retcode %s' % (' '.join(cmd), retcode,)
+            )
+
+
+class ConfigurationException(Exception):
+    pass
+
+
+def read_git_output(args, input=None, keepends=False, **kw):
+    """Read the output of a Git command."""
+
+    return read_output(
+        ['git', '-c', 'i18n.logoutputencoding=%s' % (ENCODING,)] + args,
+        input=input, keepends=keepends, **kw
+        )
+
+
+def read_output(cmd, input=None, keepends=False, **kw):
+    if input:
+        stdin = subprocess.PIPE
+    else:
+        stdin = None
+    p = subprocess.Popen(
+        cmd, stdin=stdin, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kw
+        )
+    (out, err) = p.communicate(input)
+    retcode = p.wait()
+    if retcode:
+        raise CommandError(cmd, retcode)
+    if not keepends:
+        out = out.rstrip('\n\r')
+    return out
+
+
+def read_git_lines(args, keepends=False, **kw):
+    """Return the lines output by Git command.
+
+    Return as single lines, with newlines stripped off."""
+
+    return read_git_output(args, keepends=True, **kw).splitlines(keepends)
+
+
+class Config(object):
+    def __init__(self, section, git_config=None):
+        """Represent a section of the git configuration.
+
+        If git_config is specified, it is passed to "git config" in
+        the GIT_CONFIG environment variable, meaning that "git config"
+        will read the specified path rather than the Git default
+        config paths."""
+
+        self.section = section
+        if git_config:
+            self.env = os.environ.copy()
+            self.env['GIT_CONFIG'] = git_config
+        else:
+            self.env = None
+
+    @staticmethod
+    def _split(s):
+        """Split NUL-terminated values."""
+
+        words = s.split('\0')
+        assert words[-1] == ''
+        return words[:-1]
+
+    def get(self, name, default=None):
+        try:
+            values = self._split(read_git_output(
+                    ['config', '--get', '--null', '%s.%s' % (self.section, name)],
+                    env=self.env, keepends=True,
+                    ))
+            assert len(values) == 1
+            return values[0]
+        except CommandError:
+            return default
+
+    def get_bool(self, name, default=None):
+        try:
+            value = read_git_output(
+                ['config', '--get', '--bool', '%s.%s' % (self.section, name)],
+                env=self.env,
+                )
+        except CommandError:
+            return default
+        return value == 'true'
+
+    def get_all(self, name, default=None):
+        """Read a (possibly multivalued) setting from the configuration.
+
+        Return the result as a list of values, or default if the name
+        is unset."""
+
+        try:
+            return self._split(read_git_output(
+                ['config', '--get-all', '--null', '%s.%s' % (self.section, name)],
+                env=self.env, keepends=True,
+                ))
+        except CommandError, e:
+            if e.retcode == 1:
+                # "the section or key is invalid"; i.e., there is no
+                # value for the specified key.
+                return default
+            else:
+                raise
+
+    def get_recipients(self, name, default=None):
+        """Read a recipients list from the configuration.
+
+        Return the result as a comma-separated list of email
+        addresses, or default if the option is unset.  If the setting
+        has multiple values, concatenate them with comma separators."""
+
+        lines = self.get_all(name, default=None)
+        if lines is None:
+            return default
+        return ', '.join(line.strip() for line in lines)
+
+    def set(self, name, value):
+        read_git_output(
+            ['config', '%s.%s' % (self.section, name), value],
+            env=self.env,
+            )
+
+    def add(self, name, value):
+        read_git_output(
+            ['config', '--add', '%s.%s' % (self.section, name), value],
+            env=self.env,
+            )
+
+    def has_key(self, name):
+        return self.get_all(name, default=None) is not None
+
+    def unset_all(self, name):
+        try:
+            read_git_output(
+                ['config', '--unset-all', '%s.%s' % (self.section, name)],
+                env=self.env,
+                )
+        except CommandError, e:
+            if e.retcode == 5:
+                # The name doesn't exist, which is what we wanted anyway...
+                pass
+            else:
+                raise
+
+    def set_recipients(self, name, value):
+        self.unset_all(name)
+        for pair in getaddresses([value]):
+            self.add(name, formataddr(pair))
+
+
+def generate_summaries(*log_args):
+    """Generate a brief summary for each revision requested.
+
+    log_args are strings that will be passed directly to "git log" as
+    revision selectors.  Iterate over (sha1_short, subject) for each
+    commit specified by log_args (subject is the first line of the
+    commit message as a string without EOLs)."""
+
+    cmd = [
+        'log', '--abbrev', '--format=%h %s',
+        ] + list(log_args) + ['--']
+    for line in read_git_lines(cmd):
+        yield tuple(line.split(' ', 1))
+
+
+def limit_lines(lines, max_lines):
+    for (index, line) in enumerate(lines):
+        if index < max_lines:
+            yield line
+
+    if index >= max_lines:
+        yield '... %d lines suppressed ...\n' % (index + 1 - max_lines,)
+
+
+def limit_linelength(lines, max_linelength):
+    for line in lines:
+        # Don't forget that lines always include a trailing newline.
+        if len(line) > max_linelength + 1:
+            line = line[:max_linelength - 7] + ' [...]\n'
+        yield line
+
+
+class CommitSet(object):
+    """A (constant) set of object names.
+
+    The set should be initialized with full SHA1 object names.  The
+    __contains__() method returns True iff its argument is an
+    abbreviation of any the names in the set."""
+
+    def __init__(self, names):
+        self._names = sorted(names)
+
+    def __len__(self):
+        return len(self._names)
+
+    def __contains__(self, sha1_abbrev):
+        """Return True iff this set contains sha1_abbrev (which might be abbreviated)."""
+
+        i = bisect.bisect_left(self._names, sha1_abbrev)
+        return i < len(self) and self._names[i].startswith(sha1_abbrev)
+
+
+class GitObject(object):
+    def __init__(self, sha1, type=None):
+        if sha1 == ZEROS:
+            self.sha1 = self.type = self.commit_sha1 = None
+        else:
+            self.sha1 = sha1
+            self.type = type or read_git_output(['cat-file', '-t', self.sha1])
+
+            if self.type == 'commit':
+                self.commit_sha1 = self.sha1
+            elif self.type == 'tag':
+                try:
+                    self.commit_sha1 = read_git_output(
+                        ['rev-parse', '--verify', '%s^0' % (self.sha1,)]
+                        )
+                except CommandError:
+                    # Cannot deref tag to determine commit_sha1
+                    self.commit_sha1 = None
+            else:
+                self.commit_sha1 = None
+
+        self.short = read_git_output(['rev-parse', '--short', sha1])
+
+    def get_summary(self):
+        """Return (sha1_short, subject) for this commit."""
+
+        if not self.sha1:
+            raise ValueError('Empty commit has no summary')
+
+        return iter(generate_summaries('--no-walk', self.sha1)).next()
+
+    def __eq__(self, other):
+        return isinstance(other, GitObject) and self.sha1 == other.sha1
+
+    def __hash__(self):
+        return hash(self.sha1)
+
+    def __nonzero__(self):
+        return bool(self.sha1)
+
+    def __str__(self):
+        return self.sha1 or ZEROS
+
+
+class Change(object):
+    """A Change that has been made to the Git repository.
+
+    Abstract class from which both Revisions and ReferenceChanges are
+    derived.  A Change knows how to generate a notification email
+    describing itself."""
+
+    def __init__(self, environment):
+        self.environment = environment
+        self._values = None
+
+    def _compute_values(self):
+        """Return a dictionary {keyword : expansion} for this Change.
+
+        Derived classes overload this method to add more entries to
+        the return value.  This method is used internally by
+        get_values().  The return value should always be a new
+        dictionary."""
+
+        return self.environment.get_values()
+
+    def get_values(self, **extra_values):
+        """Return a dictionary {keyword : expansion} for this Change.
+
+        Return a dictionary mapping keywords to the values that they
+        should be expanded to for this Change (used when interpolating
+        template strings).  If any keyword arguments are supplied, add
+        those to the return value as well.  The return value is always
+        a new dictionary."""
+
+        if self._values is None:
+            self._values = self._compute_values()
+
+        values = self._values.copy()
+        if extra_values:
+            values.update(extra_values)
+        return values
+
+    def expand(self, template, **extra_values):
+        """Expand template.
+
+        Expand the template (which should be a string) using string
+        interpolation of the values for this Change.  If any keyword
+        arguments are provided, also include those in the keywords
+        available for interpolation."""
+
+        return template % self.get_values(**extra_values)
+
+    def expand_lines(self, template, **extra_values):
+        """Break template into lines and expand each line."""
+
+        values = self.get_values(**extra_values)
+        for line in template.splitlines(True):
+            yield line % values
+
+    def expand_header_lines(self, template, **extra_values):
+        """Break template into lines and expand each line as an RFC 2822 header.
+
+        Encode values and split up lines that are too long.  Silently
+        skip lines that contain references to unknown variables."""
+
+        values = self.get_values(**extra_values)
+        for line in template.splitlines():
+            (name, value) = line.split(':', 1)
+
+            try:
+                value = value % values
+            except KeyError, e:
+                if DEBUG:
+                    sys.stderr.write(
+                        'Warning: unknown variable %r in the following line; line skipped:\n'
+                        '    %s\n'
+                        % (e.args[0], line,)
+                        )
+            else:
+                try:
+                    h = Header(value, header_name=name)
+                except UnicodeDecodeError:
+                    h = Header(value, header_name=name, charset=CHARSET, errors='replace')
+                for splitline in ('%s: %s\n' % (name, h.encode(),)).splitlines(True):
+                    yield splitline
+
+    def generate_email_header(self):
+        """Generate the RFC 2822 email headers for this Change, a line at a time.
+
+        The output should not include the trailing blank line."""
+
+        raise NotImplementedError()
+
+    def generate_email_intro(self):
+        """Generate the email intro for this Change, a line at a time.
+
+        The output will be used as the standard boilerplate at the top
+        of the email body."""
+
+        raise NotImplementedError()
+
+    def generate_email_body(self):
+        """Generate the main part of the email body, a line at a time.
+
+        The text in the body might be truncated after a specified
+        number of lines (see multimailhook.emailmaxlines)."""
+
+        raise NotImplementedError()
+
+    def generate_email_footer(self):
+        """Generate the footer of the email, a line at a time.
+
+        The footer is always included, irrespective of
+        multimailhook.emailmaxlines."""
+
+        raise NotImplementedError()
+
+    def generate_email(self, push, body_filter=None):
+        """Generate an email describing this change.
+
+        Iterate over the lines (including the header lines) of an
+        email describing this change.  If body_filter is not None,
+        then use it to filter the lines that are intended for the
+        email body."""
+
+        for line in self.generate_email_header():
+            yield line
+        yield '\n'
+        for line in self.generate_email_intro():
+            yield line
+
+        body = self.generate_email_body(push)
+        if body_filter is not None:
+            body = body_filter(body)
+        for line in body:
+            yield line
+
+        for line in self.generate_email_footer():
+            yield line
+
+
+class Revision(Change):
+    """A Change consisting of a single git commit."""
+
+    def __init__(self, reference_change, rev, num, tot):
+        Change.__init__(self, reference_change.environment)
+        self.reference_change = reference_change
+        self.rev = rev
+        self.change_type = self.reference_change.change_type
+        self.refname = self.reference_change.refname
+        self.num = num
+        self.tot = tot
+        self.author = read_git_output(['log', '--no-walk', '--format=%aN <%aE>', self.rev.sha1])
+        self.recipients = self.environment.get_revision_recipients(self)
+
+    def _compute_values(self):
+        values = Change._compute_values(self)
+
+        oneline = read_git_output(
+            ['log', '--format=%s', '--no-walk', self.rev.sha1]
+            )
+
+        values['rev'] = self.rev.sha1
+        values['rev_short'] = self.rev.short
+        values['change_type'] = self.change_type
+        values['refname'] = self.refname
+        values['short_refname'] = self.reference_change.short_refname
+        values['refname_type'] = self.reference_change.refname_type
+        values['reply_to_msgid'] = self.reference_change.msgid
+        values['num'] = self.num
+        values['tot'] = self.tot
+        values['recipients'] = self.recipients
+        values['oneline'] = oneline
+        values['author'] = self.author
+
+        reply_to = self.environment.get_reply_to_commit(self)
+        if reply_to:
+            values['reply_to'] = reply_to
+
+        return values
+
+    def generate_email_header(self):
+        for line in self.expand_header_lines(REVISION_HEADER_TEMPLATE):
+            yield line
+
+    def generate_email_intro(self):
+        for line in self.expand_lines(REVISION_INTRO_TEMPLATE):
+            yield line
+
+    def generate_email_body(self, push):
+        """Show this revision."""
+
+        return read_git_lines(
+            [
+                'log', '-C',
+                 '--stat', '-p', '--cc',
+                '-1', self.rev.sha1,
+                ],
+            keepends=True,
+            )
+
+    def generate_email_footer(self):
+        return self.expand_lines(REVISION_FOOTER_TEMPLATE)
+
+
+class ReferenceChange(Change):
+    """A Change to a Git reference.
+
+    An abstract class representing a create, update, or delete of a
+    Git reference.  Derived classes handle specific types of reference
+    (e.g., tags vs. branches).  These classes generate the main
+    reference change email summarizing the reference change and
+    whether it caused any any commits to be added or removed.
+
+    ReferenceChange objects are usually created using the static
+    create() method, which has the logic to decide which derived class
+    to instantiate."""
+
+    REF_RE = re.compile(r'^refs\/(?P<area>[^\/]+)\/(?P<shortname>.*)$')
+
+    @staticmethod
+    def create(environment, oldrev, newrev, refname):
+        """Return a ReferenceChange object representing the change.
+
+        Return an object that represents the type of change that is being
+        made. oldrev and newrev should be SHA1s or ZEROS."""
+
+        old = GitObject(oldrev)
+        new = GitObject(newrev)
+        rev = new or old
+
+        # The revision type tells us what type the commit is, combined with
+        # the location of the ref we can decide between
+        #  - working branch
+        #  - tracking branch
+        #  - unannotated tag
+        #  - annotated tag
+        m = ReferenceChange.REF_RE.match(refname)
+        if m:
+            area = m.group('area')
+            short_refname = m.group('shortname')
+        else:
+            area = ''
+            short_refname = refname
+
+        if rev.type == 'tag':
+            # Annotated tag:
+            klass = AnnotatedTagChange
+        elif rev.type == 'commit':
+            if area == 'tags':
+                # Non-annotated tag:
+                klass = NonAnnotatedTagChange
+            elif area == 'heads':
+                # Branch:
+                klass = BranchChange
+            elif area == 'remotes':
+                # Tracking branch:
+                sys.stderr.write(
+                    '*** Push-update of tracking branch %r\n'
+                    '***  - incomplete email generated.\n'
+                     % (refname,)
+                    )
+                klass = OtherReferenceChange
+            else:
+                # Some other reference namespace:
+                sys.stderr.write(
+                    '*** Push-update of strange reference %r\n'
+                    '***  - incomplete email generated.\n'
+                     % (refname,)
+                    )
+                klass = OtherReferenceChange
+        else:
+            # Anything else (is there anything else?)
+            sys.stderr.write(
+                '*** Unknown type of update to %r (%s)\n'
+                '***  - incomplete email generated.\n'
+                 % (refname, rev.type,)
+                )
+            klass = OtherReferenceChange
+
+        return klass(
+            environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        Change.__init__(self, environment)
+        self.change_type = {
+            (False, True) : 'create',
+            (True, True) : 'update',
+            (True, False) : 'delete',
+            }[bool(old), bool(new)]
+        self.refname = refname
+        self.short_refname = short_refname
+        self.old = old
+        self.new = new
+        self.rev = rev
+        self.msgid = make_msgid()
+        self.diffopts = environment.diffopts
+        self.logopts = environment.logopts
+        self.showlog = environment.refchange_showlog
+
+    def _compute_values(self):
+        values = Change._compute_values(self)
+
+        values['change_type'] = self.change_type
+        values['refname_type'] = self.refname_type
+        values['refname'] = self.refname
+        values['short_refname'] = self.short_refname
+        values['msgid'] = self.msgid
+        values['recipients'] = self.recipients
+        values['oldrev'] = str(self.old)
+        values['oldrev_short'] = self.old.short
+        values['newrev'] = str(self.new)
+        values['newrev_short'] = self.new.short
+
+        if self.old:
+            values['oldrev_type'] = self.old.type
+        if self.new:
+            values['newrev_type'] = self.new.type
+
+        reply_to = self.environment.get_reply_to_refchange(self)
+        if reply_to:
+            values['reply_to'] = reply_to
+
+        return values
+
+    def get_subject(self):
+        template = {
+            'create' : REF_CREATED_SUBJECT_TEMPLATE,
+            'update' : REF_UPDATED_SUBJECT_TEMPLATE,
+            'delete' : REF_DELETED_SUBJECT_TEMPLATE,
+            }[self.change_type]
+        return self.expand(template)
+
+    def generate_email_header(self):
+        for line in self.expand_header_lines(
+            REFCHANGE_HEADER_TEMPLATE, subject=self.get_subject(),
+            ):
+            yield line
+
+    def generate_email_intro(self):
+        for line in self.expand_lines(REFCHANGE_INTRO_TEMPLATE):
+            yield line
+
+    def generate_email_body(self, push):
+        """Call the appropriate body-generation routine.
+
+        Call one of generate_create_summary() /
+        generate_update_summary() / generate_delete_summary()."""
+
+        change_summary = {
+            'create' : self.generate_create_summary,
+            'delete' : self.generate_delete_summary,
+            'update' : self.generate_update_summary,
+            }[self.change_type](push)
+        for line in change_summary:
+            yield line
+
+        for line in self.generate_revision_change_summary(push):
+            yield line
+
+    def generate_email_footer(self):
+        return self.expand_lines(FOOTER_TEMPLATE)
+
+    def generate_revision_change_log(self, new_commits_list):
+        if self.showlog:
+            yield '\n'
+            yield 'Detailed log of new commits:\n\n'
+            for line in read_git_lines(
+                    ['log', '--no-walk']
+                    + self.logopts
+                    + new_commits_list
+                    + ['--'],
+                    keepends=True,
+                ):
+                yield line
+
+    def generate_revision_change_summary(self, push):
+        """Generate a summary of the revisions added/removed by this change."""
+
+        if self.new.commit_sha1 and not self.old.commit_sha1:
+            # A new reference was created.  List the new revisions
+            # brought by the new reference (i.e., those revisions that
+            # were not in the repository before this reference
+            # change).
+            sha1s = list(push.get_new_commits(self))
+            sha1s.reverse()
+            tot = len(sha1s)
+            new_revisions = [
+                Revision(self, GitObject(sha1), num=i+1, tot=tot)
+                for (i, sha1) in enumerate(sha1s)
+                ]
+
+            if new_revisions:
+                yield self.expand('This %(refname_type)s includes the following new commits:\n')
+                yield '\n'
+                for r in new_revisions:
+                    (sha1, subject) = r.rev.get_summary()
+                    yield r.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action='new', text=subject,
+                        )
+                yield '\n'
+                for line in self.expand_lines(NEW_REVISIONS_TEMPLATE, tot=tot):
+                    yield line
+                for line in self.generate_revision_change_log([r.rev.sha1 for r in new_revisions]):
+                    yield line
+            else:
+                for line in self.expand_lines(NO_NEW_REVISIONS_TEMPLATE):
+                    yield line
+
+        elif self.new.commit_sha1 and self.old.commit_sha1:
+            # A reference was changed to point at a different commit.
+            # List the revisions that were removed and/or added *from
+            # that reference* by this reference change, along with a
+            # diff between the trees for its old and new values.
+
+            # List of the revisions that were added to the branch by
+            # this update.  Note this list can include revisions that
+            # have already had notification emails; we want such
+            # revisions in the summary even though we will not send
+            # new notification emails for them.
+            adds = list(generate_summaries(
+                    '--topo-order', '--reverse', '%s..%s'
+                    % (self.old.commit_sha1, self.new.commit_sha1,)
+                    ))
+
+            # List of the revisions that were removed from the branch
+            # by this update.  This will be empty except for
+            # non-fast-forward updates.
+            discards = list(generate_summaries(
+                    '%s..%s' % (self.new.commit_sha1, self.old.commit_sha1,)
+                    ))
+
+            if adds:
+                new_commits_list = push.get_new_commits(self)
+            else:
+                new_commits_list = []
+            new_commits = CommitSet(new_commits_list)
+
+            if discards:
+                discarded_commits = CommitSet(push.get_discarded_commits(self))
+            else:
+                discarded_commits = CommitSet([])
+
+            if discards and adds:
+                for (sha1, subject) in discards:
+                    if sha1 in discarded_commits:
+                        action = 'discards'
+                    else:
+                        action = 'omits'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                for (sha1, subject) in adds:
+                    if sha1 in new_commits:
+                        action = 'new'
+                    else:
+                        action = 'adds'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                yield '\n'
+                for line in self.expand_lines(NON_FF_TEMPLATE):
+                    yield line
+
+            elif discards:
+                for (sha1, subject) in discards:
+                    if sha1 in discarded_commits:
+                        action = 'discards'
+                    else:
+                        action = 'omits'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+                yield '\n'
+                for line in self.expand_lines(REWIND_ONLY_TEMPLATE):
+                    yield line
+
+            elif adds:
+                (sha1, subject) = self.old.get_summary()
+                yield self.expand(
+                    BRIEF_SUMMARY_TEMPLATE, action='from',
+                    rev_short=sha1, text=subject,
+                    )
+                for (sha1, subject) in adds:
+                    if sha1 in new_commits:
+                        action = 'new'
+                    else:
+                        action = 'adds'
+                    yield self.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action=action,
+                        rev_short=sha1, text=subject,
+                        )
+
+            yield '\n'
+
+            if new_commits:
+                for line in self.expand_lines(NEW_REVISIONS_TEMPLATE, tot=len(new_commits)):
+                    yield line
+                for line in self.generate_revision_change_log(new_commits_list):
+                    yield line
+            else:
+                for line in self.expand_lines(NO_NEW_REVISIONS_TEMPLATE):
+                    yield line
+
+            # The diffstat is shown from the old revision to the new
+            # revision.  This is to show the truth of what happened in
+            # this change.  There's no point showing the stat from the
+            # base to the new revision because the base is effectively a
+            # random revision at this point - the user will be interested
+            # in what this revision changed - including the undoing of
+            # previous revisions in the case of non-fast-forward updates.
+            yield '\n'
+            yield 'Summary of changes:\n'
+            for line in read_git_lines(
+                ['diff-tree']
+                + self.diffopts
+                + ['%s..%s' % (self.old.commit_sha1, self.new.commit_sha1,)],
+                keepends=True,
+                ):
+                yield line
+
+        elif self.old.commit_sha1 and not self.new.commit_sha1:
+            # A reference was deleted.  List the revisions that were
+            # removed from the repository by this reference change.
+
+            sha1s = list(push.get_discarded_commits(self))
+            tot = len(sha1s)
+            discarded_revisions = [
+                Revision(self, GitObject(sha1), num=i+1, tot=tot)
+                for (i, sha1) in enumerate(sha1s)
+                ]
+
+            if discarded_revisions:
+                for line in self.expand_lines(DISCARDED_REVISIONS_TEMPLATE):
+                    yield line
+                yield '\n'
+                for r in discarded_revisions:
+                    (sha1, subject) = r.rev.get_summary()
+                    yield r.expand(
+                        BRIEF_SUMMARY_TEMPLATE, action='discards', text=subject,
+                        )
+            else:
+                for line in self.expand_lines(NO_DISCARDED_REVISIONS_TEMPLATE):
+                    yield line
+
+        elif not self.old.commit_sha1 and not self.new.commit_sha1:
+            for line in self.expand_lines(NON_COMMIT_UPDATE_TEMPLATE):
+                yield line
+
+    def generate_create_summary(self, push):
+        """Called for the creation of a reference."""
+
+        # This is a new reference and so oldrev is not valid
+        (sha1, subject) = self.new.get_summary()
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='at',
+            rev_short=sha1, text=subject,
+            )
+        yield '\n'
+
+    def generate_update_summary(self, push):
+        """Called for the change of a pre-existing branch."""
+
+        return iter([])
+
+    def generate_delete_summary(self, push):
+        """Called for the deletion of any type of reference."""
+
+        (sha1, subject) = self.old.get_summary()
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='was',
+            rev_short=sha1, text=subject,
+            )
+        yield '\n'
+
+
+class BranchChange(ReferenceChange):
+    refname_type = 'branch'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+
+
+class AnnotatedTagChange(ReferenceChange):
+    refname_type = 'annotated tag'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_announce_recipients(self)
+        self.show_shortlog = environment.announce_show_shortlog
+
+    ANNOTATED_TAG_FORMAT = (
+        '%(*objectname)\n'
+        '%(*objecttype)\n'
+        '%(taggername)\n'
+        '%(taggerdate)'
+        )
+
+    def describe_tag(self, push):
+        """Describe the new value of an annotated tag."""
+
+        # Use git for-each-ref to pull out the individual fields from
+        # the tag
+        [tagobject, tagtype, tagger, tagged] = read_git_lines(
+            ['for-each-ref', '--format=%s' % (self.ANNOTATED_TAG_FORMAT,), self.refname],
+            )
+
+        yield self.expand(
+            BRIEF_SUMMARY_TEMPLATE, action='tagging',
+            rev_short=tagobject, text='(%s)' % (tagtype,),
+            )
+        if tagtype == 'commit':
+            # If the tagged object is a commit, then we assume this is a
+            # release, and so we calculate which tag this tag is
+            # replacing
+            try:
+                prevtag = read_git_output(['describe', '--abbrev=0', '%s^' % (self.new,)])
+            except CommandError:
+                prevtag = None
+            if prevtag:
+                yield '  replaces  %s\n' % (prevtag,)
+        else:
+            prevtag = None
+            yield '    length  %s bytes\n' % (read_git_output(['cat-file', '-s', tagobject]),)
+
+        yield ' tagged by  %s\n' % (tagger,)
+        yield '        on  %s\n' % (tagged,)
+        yield '\n'
+
+        # Show the content of the tag message; this might contain a
+        # change log or release notes so is worth displaying.
+        yield LOGBEGIN
+        contents = list(read_git_lines(['cat-file', 'tag', self.new.sha1], keepends=True))
+        contents = contents[contents.index('\n') + 1:]
+        if contents and contents[-1][-1:] != '\n':
+            contents.append('\n')
+        for line in contents:
+            yield line
+
+        if self.show_shortlog and tagtype == 'commit':
+            # Only commit tags make sense to have rev-list operations
+            # performed on them
+            yield '\n'
+            if prevtag:
+                # Show changes since the previous release
+                revlist = read_git_output(
+                    ['rev-list', '--pretty=short', '%s..%s' % (prevtag, self.new,)],
+                    keepends=True,
+                    )
+            else:
+                # No previous tag, show all the changes since time
+                # began
+                revlist = read_git_output(
+                    ['rev-list', '--pretty=short', '%s' % (self.new,)],
+                    keepends=True,
+                    )
+            for line in read_git_lines(['shortlog'], input=revlist, keepends=True):
+                yield line
+
+        yield LOGEND
+        yield '\n'
+
+    def generate_create_summary(self, push):
+        """Called for the creation of an annotated tag."""
+
+        for line in self.expand_lines(TAG_CREATED_TEMPLATE):
+            yield line
+
+        for line in self.describe_tag(push):
+            yield line
+
+    def generate_update_summary(self, push):
+        """Called for the update of an annotated tag.
+
+        This is probably a rare event and may not even be allowed."""
+
+        for line in self.expand_lines(TAG_UPDATED_TEMPLATE):
+            yield line
+
+        for line in self.describe_tag(push):
+            yield line
+
+    def generate_delete_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_DELETED_TEMPLATE):
+            yield line
+
+        yield self.expand('   tag was  %(oldrev_short)s\n')
+        yield '\n'
+
+
+class NonAnnotatedTagChange(ReferenceChange):
+    refname_type = 'tag'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=short_refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+
+    def generate_create_summary(self, push):
+        """Called for the creation of an annotated tag."""
+
+        for line in self.expand_lines(TAG_CREATED_TEMPLATE):
+            yield line
+
+    def generate_update_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_UPDATED_TEMPLATE):
+            yield line
+
+    def generate_delete_summary(self, push):
+        """Called when a non-annotated reference is updated."""
+
+        for line in self.expand_lines(TAG_DELETED_TEMPLATE):
+            yield line
+
+        for line in ReferenceChange.generate_delete_summary(self, push):
+            yield line
+
+
+class OtherReferenceChange(ReferenceChange):
+    refname_type = 'reference'
+
+    def __init__(self, environment, refname, short_refname, old, new, rev):
+        # We use the full refname as short_refname, because otherwise
+        # the full name of the reference would not be obvious from the
+        # text of the email.
+        ReferenceChange.__init__(
+            self, environment,
+            refname=refname, short_refname=refname,
+            old=old, new=new, rev=rev,
+            )
+        self.recipients = environment.get_refchange_recipients(self)
+
+
+class Mailer(object):
+    """An object that can send emails."""
+
+    def send(self, lines, to_addrs):
+        """Send an email consisting of lines.
+
+        lines must be an iterable over the lines constituting the
+        header and body of the email.  to_addrs is a list of recipient
+        addresses (can be needed even if lines already contains a
+        "To:" field).  It can be either a string (comma-separated list
+        of email addresses) or a Python list of individual email
+        addresses.
+
+        """
+
+        raise NotImplementedError()
+
+
+class SendMailer(Mailer):
+    """Send emails using 'sendmail -t'."""
+
+    SENDMAIL_CANDIDATES = [
+        '/usr/sbin/sendmail',
+        '/usr/lib/sendmail',
+        ]
+
+    @staticmethod
+    def find_sendmail():
+        for path in SendMailer.SENDMAIL_CANDIDATES:
+            if os.access(path, os.X_OK):
+                return path
+        else:
+            raise ConfigurationException(
+                'No sendmail executable found.  '
+                'Try setting multimailhook.sendmailCommand.'
+                )
+
+    def __init__(self, command=None, envelopesender=None):
+        """Construct a SendMailer instance.
+
+        command should be the command and arguments used to invoke
+        sendmail, as a list of strings.  If an envelopesender is
+        provided, it will also be passed to the command, via '-f
+        envelopesender'."""
+
+        if command:
+            self.command = command[:]
+        else:
+            self.command = [self.find_sendmail(), '-t']
+
+        if envelopesender:
+            self.command.extend(['-f', envelopesender])
+
+    def send(self, lines, to_addrs):
+        try:
+            p = subprocess.Popen(self.command, stdin=subprocess.PIPE)
+        except OSError, e:
+            sys.stderr.write(
+                '*** Cannot execute command: %s\n' % ' '.join(self.command)
+                + '*** %s\n' % str(e)
+                + '*** Try setting multimailhook.mailer to "smtp"\n'
+                '*** to send emails without using the sendmail command.\n'
+                )
+            sys.exit(1)
+        try:
+            p.stdin.writelines(lines)
+        except:
+            sys.stderr.write(
+                '*** Error while generating commit email\n'
+                '***  - mail sending aborted.\n'
+                )
+            p.terminate()
+            raise
+        else:
+            p.stdin.close()
+            retcode = p.wait()
+            if retcode:
+                raise CommandError(self.command, retcode)
+
+
+class SMTPMailer(Mailer):
+    """Send emails using Python's smtplib."""
+
+    def __init__(self, envelopesender, smtpserver):
+        if not envelopesender:
+            sys.stderr.write(
+                'fatal: git_multimail: cannot use SMTPMailer without a sender address.\n'
+                'please set either multimailhook.envelopeSender or user.email\n'
+                )
+            sys.exit(1)
+        self.envelopesender = envelopesender
+        self.smtpserver = smtpserver
+        try:
+            self.smtp = smtplib.SMTP(self.smtpserver)
+        except Exception, e:
+            sys.stderr.write('*** Error establishing SMTP connection to %s***\n' % self.smtpserver)
+            sys.stderr.write('*** %s\n' % str(e))
+            sys.exit(1)
+
+    def __del__(self):
+        self.smtp.quit()
+
+    def send(self, lines, to_addrs):
+        try:
+            msg = ''.join(lines)
+            # turn comma-separated list into Python list if needed.
+            if isinstance(to_addrs, basestring):
+                to_addrs = [email for (name, email) in getaddresses([to_addrs])]
+            self.smtp.sendmail(self.envelopesender, to_addrs, msg)
+        except Exception, e:
+            sys.stderr.write('*** Error sending email***\n')
+            sys.stderr.write('*** %s\n' % str(e))
+            self.smtp.quit()
+            sys.exit(1)
+
+
+class OutputMailer(Mailer):
+    """Write emails to an output stream, bracketed by lines of '=' characters.
+
+    This is intended for debugging purposes."""
+
+    SEPARATOR = '=' * 75 + '\n'
+
+    def __init__(self, f):
+        self.f = f
+
+    def send(self, lines, to_addrs):
+        self.f.write(self.SEPARATOR)
+        self.f.writelines(lines)
+        self.f.write(self.SEPARATOR)
+
+
+def get_git_dir():
+    """Determine GIT_DIR.
+
+    Determine GIT_DIR either from the GIT_DIR environment variable or
+    from the working directory, using Git's usual rules."""
+
+    try:
+        return read_git_output(['rev-parse', '--git-dir'])
+    except CommandError:
+        sys.stderr.write('fatal: git_multimail: not in a git directory\n')
+        sys.exit(1)
+
+
+class Environment(object):
+    """Describes the environment in which the push is occurring.
+
+    An Environment object encapsulates information about the local
+    environment.  For example, it knows how to determine:
+
+    * the name of the repository to which the push occurred
+
+    * what user did the push
+
+    * what users want to be informed about various types of changes.
+
+    An Environment object is expected to have the following methods:
+
+        get_repo_shortname()
+
+            Return a short name for the repository, for display
+            purposes.
+
+        get_repo_path()
+
+            Return the absolute path to the Git repository.
+
+        get_emailprefix()
+
+            Return a string that will be prefixed to every email's
+            subject.
+
+        get_pusher()
+
+            Return the username of the person who pushed the changes.
+            This value is used in the email body to indicate who
+            pushed the change.
+
+        get_pusher_email() (may return None)
+
+            Return the email address of the person who pushed the
+            changes.  The value should be a single RFC 2822 email
+            address as a string; e.g., "Joe User <user@example.com>"
+            if available, otherwise "user@example.com".  If set, the
+            value is used as the Reply-To address for refchange
+            emails.  If it is impossible to determine the pusher's
+            email, this attribute should be set to None (in which case
+            no Reply-To header will be output).
+
+        get_sender()
+
+            Return the address to be used as the 'From' email address
+            in the email envelope.
+
+        get_fromaddr()
+
+            Return the 'From' email address used in the email 'From:'
+            headers.  (May be a full RFC 2822 email address like 'Joe
+            User <user@example.com>'.)
+
+        get_administrator()
+
+            Return the name and/or email of the repository
+            administrator.  This value is used in the footer as the
+            person to whom requests to be removed from the
+            notification list should be sent.  Ideally, it should
+            include a valid email address.
+
+        get_reply_to_refchange()
+        get_reply_to_commit()
+
+            Return the address to use in the email "Reply-To" header,
+            as a string.  These can be an RFC 2822 email address, or
+            None to omit the "Reply-To" header.
+            get_reply_to_refchange() is used for refchange emails;
+            get_reply_to_commit() is used for individual commit
+            emails.
+
+    They should also define the following attributes:
+
+        announce_show_shortlog (bool)
+
+            True iff announce emails should include a shortlog.
+
+        refchange_showlog (bool)
+
+            True iff refchanges emails should include a detailed log.
+
+        diffopts (list of strings)
+
+            The options that should be passed to 'git diff' for the
+            summary email.  The value should be a list of strings
+            representing words to be passed to the command.
+
+        logopts (list of strings)
+
+            Analogous to diffopts, but contains options passed to
+            'git log' when generating the detailed log for a set of
+            commits (see refchange_showlog)
+
+    """
+
+    REPO_NAME_RE = re.compile(r'^(?P<name>.+?)(?:\.git)$')
+
+    def __init__(self, osenv=None):
+        self.osenv = osenv or os.environ
+        self.announce_show_shortlog = False
+        self.maxcommitemails = 500
+        self.diffopts = ['--stat', '--summary', '--find-copies-harder']
+        self.logopts = []
+        self.refchange_showlog = False
+
+        self.COMPUTED_KEYS = [
+            'administrator',
+            'charset',
+            'emailprefix',
+            'fromaddr',
+            'pusher',
+            'pusher_email',
+            'repo_path',
+            'repo_shortname',
+            'sender',
+            ]
+
+        self._values = None
+
+    def get_repo_shortname(self):
+        """Use the last part of the repo path, with ".git" stripped off if present."""
+
+        basename = os.path.basename(os.path.abspath(self.get_repo_path()))
+        m = self.REPO_NAME_RE.match(basename)
+        if m:
+            return m.group('name')
+        else:
+            return basename
+
+    def get_pusher(self):
+        raise NotImplementedError()
+
+    def get_pusher_email(self):
+        return None
+
+    def get_administrator(self):
+        return 'the administrator of this repository'
+
+    def get_emailprefix(self):
+        return ''
+
+    def get_repo_path(self):
+        if read_git_output(['rev-parse', '--is-bare-repository']) == 'true':
+            path = get_git_dir()
+        else:
+            path = read_git_output(['rev-parse', '--show-toplevel'])
+        return os.path.abspath(path)
+
+    def get_charset(self):
+        return CHARSET
+
+    def get_values(self):
+        """Return a dictionary {keyword : expansion} for this Environment.
+
+        This method is called by Change._compute_values().  The keys
+        in the returned dictionary are available to be used in any of
+        the templates.  The dictionary is created by calling
+        self.get_NAME() for each of the attributes named in
+        COMPUTED_KEYS and recording those that do not return None.
+        The return value is always a new dictionary."""
+
+        if self._values is None:
+            values = {}
+
+            for key in self.COMPUTED_KEYS:
+                value = getattr(self, 'get_%s' % (key,))()
+                if value is not None:
+                    values[key] = value
+
+            self._values = values
+
+        return self._values.copy()
+
+    def get_refchange_recipients(self, refchange):
+        """Return the recipients for notifications about refchange.
+
+        Return the list of email addresses to which notifications
+        about the specified ReferenceChange should be sent."""
+
+        raise NotImplementedError()
+
+    def get_announce_recipients(self, annotated_tag_change):
+        """Return the recipients for notifications about annotated_tag_change.
+
+        Return the list of email addresses to which notifications
+        about the specified AnnotatedTagChange should be sent."""
+
+        raise NotImplementedError()
+
+    def get_reply_to_refchange(self, refchange):
+        return self.get_pusher_email()
+
+    def get_revision_recipients(self, revision):
+        """Return the recipients for messages about revision.
+
+        Return the list of email addresses to which notifications
+        about the specified Revision should be sent.  This method
+        could be overridden, for example, to take into account the
+        contents of the revision when deciding whom to notify about
+        it.  For example, there could be a scheme for users to express
+        interest in particular files or subdirectories, and only
+        receive notification emails for revisions that affecting those
+        files."""
+
+        raise NotImplementedError()
+
+    def get_reply_to_commit(self, revision):
+        return revision.author
+
+    def filter_body(self, lines):
+        """Filter the lines intended for an email body.
+
+        lines is an iterable over the lines that would go into the
+        email body.  Filter it (e.g., limit the number of lines, the
+        line length, character set, etc.), returning another iterable.
+        See FilterLinesEnvironmentMixin and MaxlinesEnvironmentMixin
+        for classes implementing this functionality."""
+
+        return lines
+
+
+class ConfigEnvironmentMixin(Environment):
+    """A mixin that sets self.config to its constructor's config argument.
+
+    This class's constructor consumes the "config" argument.
+
+    Mixins that need to inspect the config should inherit from this
+    class (1) to make sure that "config" is still in the constructor
+    arguments with its own constructor runs and/or (2) to be sure that
+    self.config is set after construction."""
+
+    def __init__(self, config, **kw):
+        super(ConfigEnvironmentMixin, self).__init__(**kw)
+        self.config = config
+
+
+class ConfigOptionsEnvironmentMixin(ConfigEnvironmentMixin):
+    """An Environment that reads most of its information from "git config"."""
+
+    def __init__(self, config, **kw):
+        super(ConfigOptionsEnvironmentMixin, self).__init__(
+            config=config, **kw
+            )
+
+        self.announce_show_shortlog = config.get_bool(
+            'announceshortlog', default=self.announce_show_shortlog
+            )
+
+        self.refchange_showlog = config.get_bool(
+            'refchangeshowlog', default=self.refchange_showlog
+            )
+
+        maxcommitemails = config.get('maxcommitemails')
+        if maxcommitemails is not None:
+            try:
+                self.maxcommitemails = int(maxcommitemails)
+            except ValueError:
+                sys.stderr.write(
+                    '*** Malformed value for multimailhook.maxCommitEmails: %s\n' % maxcommitemails
+                    + '*** Expected a number.  Ignoring.\n'
+                    )
+
+        diffopts = config.get('diffopts')
+        if diffopts is not None:
+            self.diffopts = shlex.split(diffopts)
+
+        logopts = config.get('logopts')
+        if logopts is not None:
+            self.logopts = shlex.split(logopts)
+
+        reply_to = config.get('replyTo')
+        self.__reply_to_refchange = config.get('replyToRefchange', default=reply_to)
+        if (
+            self.__reply_to_refchange is not None
+            and self.__reply_to_refchange.lower() == 'author'
+            ):
+            raise ConfigurationException(
+                '"author" is not an allowed setting for replyToRefchange'
+                )
+        self.__reply_to_commit = config.get('replyToCommit', default=reply_to)
+
+    def get_administrator(self):
+        return (
+            self.config.get('administrator')
+            or self.get_sender()
+            or super(ConfigOptionsEnvironmentMixin, self).get_administrator()
+            )
+
+    def get_repo_shortname(self):
+        return (
+            self.config.get('reponame')
+            or super(ConfigOptionsEnvironmentMixin, self).get_repo_shortname()
+            )
+
+    def get_emailprefix(self):
+        emailprefix = self.config.get('emailprefix')
+        if emailprefix and emailprefix.strip():
+            return emailprefix.strip() + ' '
+        else:
+            return '[%s] ' % (self.get_repo_shortname(),)
+
+    def get_sender(self):
+        return self.config.get('envelopesender')
+
+    def get_fromaddr(self):
+        fromaddr = self.config.get('from')
+        if fromaddr:
+            return fromaddr
+        else:
+            config = Config('user')
+            fromname = config.get('name', default='')
+            fromemail = config.get('email', default='')
+            if fromemail:
+                return formataddr([fromname, fromemail])
+            else:
+                return self.get_sender()
+
+    def get_reply_to_refchange(self, refchange):
+        if self.__reply_to_refchange is None:
+            return super(ConfigOptionsEnvironmentMixin, self).get_reply_to_refchange(refchange)
+        elif self.__reply_to_refchange.lower() == 'pusher':
+            return self.get_pusher_email()
+        elif self.__reply_to_refchange.lower() == 'none':
+            return None
+        else:
+            return self.__reply_to_refchange
+
+    def get_reply_to_commit(self, revision):
+        if self.__reply_to_commit is None:
+            return super(ConfigOptionsEnvironmentMixin, self).get_reply_to_commit(revision)
+        elif self.__reply_to_commit.lower() == 'author':
+            return revision.get_author()
+        elif self.__reply_to_commit.lower() == 'pusher':
+            return self.get_pusher_email()
+        elif self.__reply_to_commit.lower() == 'none':
+            return None
+        else:
+            return self.__reply_to_commit
+
+
+class FilterLinesEnvironmentMixin(Environment):
+    """Handle encoding and maximum line length of body lines.
+
+        emailmaxlinelength (int or None)
+
+            The maximum length of any single line in the email body.
+            Longer lines are truncated at that length with ' [...]'
+            appended.
+
+        strict_utf8 (bool)
+
+            If this field is set to True, then the email body text is
+            expected to be UTF-8.  Any invalid characters are
+            converted to U+FFFD, the Unicode replacement character
+            (encoded as UTF-8, of course).
+
+    """
+
+    def __init__(self, strict_utf8=True, emailmaxlinelength=500, **kw):
+        super(FilterLinesEnvironmentMixin, self).__init__(**kw)
+        self.__strict_utf8 = strict_utf8
+        self.__emailmaxlinelength = emailmaxlinelength
+
+    def filter_body(self, lines):
+        lines = super(FilterLinesEnvironmentMixin, self).filter_body(lines)
+        if self.__strict_utf8:
+            lines = (line.decode(ENCODING, 'replace') for line in lines)
+            # Limit the line length in Unicode-space to avoid
+            # splitting characters:
+            if self.__emailmaxlinelength:
+                lines = limit_linelength(lines, self.__emailmaxlinelength)
+            lines = (line.encode(ENCODING, 'replace') for line in lines)
+        elif self.__emailmaxlinelength:
+            lines = limit_linelength(lines, self.__emailmaxlinelength)
+
+        return lines
+
+
+class ConfigFilterLinesEnvironmentMixin(
+    ConfigEnvironmentMixin,
+    FilterLinesEnvironmentMixin,
+    ):
+    """Handle encoding and maximum line length based on config."""
+
+    def __init__(self, config, **kw):
+        strict_utf8 = config.get_bool('emailstrictutf8', default=None)
+        if strict_utf8 is not None:
+            kw['strict_utf8'] = strict_utf8
+
+        emailmaxlinelength = config.get('emailmaxlinelength')
+        if emailmaxlinelength is not None:
+            kw['emailmaxlinelength'] = int(emailmaxlinelength)
+
+        super(ConfigFilterLinesEnvironmentMixin, self).__init__(
+            config=config, **kw
+            )
+
+
+class MaxlinesEnvironmentMixin(Environment):
+    """Limit the email body to a specified number of lines."""
+
+    def __init__(self, emailmaxlines, **kw):
+        super(MaxlinesEnvironmentMixin, self).__init__(**kw)
+        self.__emailmaxlines = emailmaxlines
+
+    def filter_body(self, lines):
+        lines = super(MaxlinesEnvironmentMixin, self).filter_body(lines)
+        if self.__emailmaxlines:
+            lines = limit_lines(lines, self.__emailmaxlines)
+        return lines
+
+
+class ConfigMaxlinesEnvironmentMixin(
+    ConfigEnvironmentMixin,
+    MaxlinesEnvironmentMixin,
+    ):
+    """Limit the email body to the number of lines specified in config."""
+
+    def __init__(self, config, **kw):
+        emailmaxlines = int(config.get('emailmaxlines', default='0'))
+        super(ConfigMaxlinesEnvironmentMixin, self).__init__(
+            config=config,
+            emailmaxlines=emailmaxlines,
+            **kw
+            )
+
+
+class PusherDomainEnvironmentMixin(ConfigEnvironmentMixin):
+    """Deduce pusher_email from pusher by appending an emaildomain."""
+
+    def __init__(self, **kw):
+        super(PusherDomainEnvironmentMixin, self).__init__(**kw)
+        self.__emaildomain = self.config.get('emaildomain')
+
+    def get_pusher_email(self):
+        if self.__emaildomain:
+            # Derive the pusher's full email address in the default way:
+            return '%s@%s' % (self.get_pusher(), self.__emaildomain)
+        else:
+            return super(PusherDomainEnvironmentMixin, self).get_pusher_email()
+
+
+class StaticRecipientsEnvironmentMixin(Environment):
+    """Set recipients statically based on constructor parameters."""
+
+    def __init__(
+        self,
+        refchange_recipients, announce_recipients, revision_recipients,
+        **kw
+        ):
+        super(StaticRecipientsEnvironmentMixin, self).__init__(**kw)
+
+        # The recipients for various types of notification emails, as
+        # RFC 2822 email addresses separated by commas (or the empty
+        # string if no recipients are configured).  Although there is
+        # a mechanism to choose the recipient lists based on on the
+        # actual *contents* of the change being reported, we only
+        # choose based on the *type* of the change.  Therefore we can
+        # compute them once and for all:
+        self.__refchange_recipients = refchange_recipients
+        self.__announce_recipients = announce_recipients
+        self.__revision_recipients = revision_recipients
+
+    def get_refchange_recipients(self, refchange):
+        return self.__refchange_recipients
+
+    def get_announce_recipients(self, annotated_tag_change):
+        return self.__announce_recipients
+
+    def get_revision_recipients(self, revision):
+        return self.__revision_recipients
+
+
+class ConfigRecipientsEnvironmentMixin(
+    ConfigEnvironmentMixin,
+    StaticRecipientsEnvironmentMixin
+    ):
+    """Determine recipients statically based on config."""
+
+    def __init__(self, config, **kw):
+        super(ConfigRecipientsEnvironmentMixin, self).__init__(
+            config=config,
+            refchange_recipients=self._get_recipients(
+                config, 'refchangelist', 'mailinglist',
+                ),
+            announce_recipients=self._get_recipients(
+                config, 'announcelist', 'refchangelist', 'mailinglist',
+                ),
+            revision_recipients=self._get_recipients(
+                config, 'commitlist', 'mailinglist',
+                ),
+            **kw
+            )
+
+    def _get_recipients(self, config, *names):
+        """Return the recipients for a particular type of message.
+
+        Return the list of email addresses to which a particular type
+        of notification email should be sent, by looking at the config
+        value for "multimailhook.$name" for each of names.  Use the
+        value from the first name that is configured.  The return
+        value is a (possibly empty) string containing RFC 2822 email
+        addresses separated by commas.  If no configuration could be
+        found, raise a ConfigurationException."""
+
+        for name in names:
+            retval = config.get_recipients(name)
+            if retval is not None:
+                return retval
+        if len(names) == 1:
+            hint = 'Please set "%s.%s"' % (config.section, name)
+        else:
+            hint = (
+                'Please set one of the following:\n    "%s"'
+                % ('"\n    "'.join('%s.%s' % (config.section, name) for name in names))
+                )
+
+        raise ConfigurationException(
+            'The list of recipients for %s is not configured.\n%s' % (names[0], hint)
+            )
+
+
+class ProjectdescEnvironmentMixin(Environment):
+    """Make a "projectdesc" value available for templates.
+
+    By default, it is set to the first line of $GIT_DIR/description
+    (if that file is present and appears to be set meaningfully)."""
+
+    def __init__(self, **kw):
+        super(ProjectdescEnvironmentMixin, self).__init__(**kw)
+        self.COMPUTED_KEYS += ['projectdesc']
+
+    def get_projectdesc(self):
+        """Return a one-line descripition of the project."""
+
+        git_dir = get_git_dir()
+        try:
+            projectdesc = open(os.path.join(git_dir, 'description')).readline().strip()
+            if projectdesc and not projectdesc.startswith('Unnamed repository'):
+                return projectdesc
+        except IOError:
+            pass
+
+        return 'UNNAMED PROJECT'
+
+
+class GenericEnvironmentMixin(Environment):
+    def get_pusher(self):
+        return self.osenv.get('USER', 'unknown user')
+
+
+class GenericEnvironment(
+    ProjectdescEnvironmentMixin,
+    ConfigMaxlinesEnvironmentMixin,
+    ConfigFilterLinesEnvironmentMixin,
+    ConfigRecipientsEnvironmentMixin,
+    PusherDomainEnvironmentMixin,
+    ConfigOptionsEnvironmentMixin,
+    GenericEnvironmentMixin,
+    Environment,
+    ):
+    pass
+
+
+class GitoliteEnvironmentMixin(Environment):
+    def get_repo_shortname(self):
+        # The gitolite environment variable $GL_REPO is a pretty good
+        # repo_shortname (though it's probably not as good as a value
+        # the user might have explicitly put in his config).
+        return (
+            self.osenv.get('GL_REPO', None)
+            or super(GitoliteEnvironmentMixin, self).get_repo_shortname()
+            )
+
+    def get_pusher(self):
+        return self.osenv.get('GL_USER', 'unknown user')
+
+
+class GitoliteEnvironment(
+    ProjectdescEnvironmentMixin,
+    ConfigMaxlinesEnvironmentMixin,
+    ConfigFilterLinesEnvironmentMixin,
+    ConfigRecipientsEnvironmentMixin,
+    PusherDomainEnvironmentMixin,
+    ConfigOptionsEnvironmentMixin,
+    GitoliteEnvironmentMixin,
+    Environment,
+    ):
+    pass
+
+
+class Push(object):
+    """Represent an entire push (i.e., a group of ReferenceChanges).
+
+    It is easy to figure out what commits were added to a *branch* by
+    a Reference change:
+
+        git rev-list change.old..change.new
+
+    or removed from a *branch*:
+
+        git rev-list change.new..change.old
+
+    But it is not quite so trivial to determine which entirely new
+    commits were added to the *repository* by a push and which old
+    commits were discarded by a push.  A big part of the job of this
+    class is to figure out these things, and to make sure that new
+    commits are only detailed once even if they were added to multiple
+    references.
+
+    The first step is to determine the "other" references--those
+    unaffected by the current push.  They are computed by
+    Push._compute_other_ref_sha1s() by listing all references then
+    removing any affected by this push.
+
+    The commits contained in the repository before this push were
+
+        git rev-list other1 other2 other3 ... change1.old change2.old ...
+
+    Where "changeN.old" is the old value of one of the references
+    affected by this push.
+
+    The commits contained in the repository after this push are
+
+        git rev-list other1 other2 other3 ... change1.new change2.new ...
+
+    The commits added by this push are the difference between these
+    two sets, which can be written
+
+        git rev-list \
+            ^other1 ^other2 ... \
+            ^change1.old ^change2.old ... \
+            change1.new change2.new ...
+
+    The commits removed by this push can be computed by
+
+        git rev-list \
+            ^other1 ^other2 ... \
+            ^change1.new ^change2.new ... \
+            change1.old change2.old ...
+
+    The last point is that it is possible that other pushes are
+    occurring simultaneously to this one, so reference values can
+    change at any time.  It is impossible to eliminate all race
+    conditions, but we reduce the window of time during which problems
+    can occur by translating reference names to SHA1s as soon as
+    possible and working with SHA1s thereafter (because SHA1s are
+    immutable)."""
+
+    # A map {(changeclass, changetype) : integer} specifying the order
+    # that reference changes will be processed if multiple reference
+    # changes are included in a single push.  The order is significant
+    # mostly because new commit notifications are threaded together
+    # with the first reference change that includes the commit.  The
+    # following order thus causes commits to be grouped with branch
+    # changes (as opposed to tag changes) if possible.
+    SORT_ORDER = dict(
+        (value, i) for (i, value) in enumerate([
+            (BranchChange, 'update'),
+            (BranchChange, 'create'),
+            (AnnotatedTagChange, 'update'),
+            (AnnotatedTagChange, 'create'),
+            (NonAnnotatedTagChange, 'update'),
+            (NonAnnotatedTagChange, 'create'),
+            (BranchChange, 'delete'),
+            (AnnotatedTagChange, 'delete'),
+            (NonAnnotatedTagChange, 'delete'),
+            (OtherReferenceChange, 'update'),
+            (OtherReferenceChange, 'create'),
+            (OtherReferenceChange, 'delete'),
+            ])
+        )
+
+    def __init__(self, changes):
+        self.changes = sorted(changes, key=self._sort_key)
+
+        # The SHA-1s of commits referred to by references unaffected
+        # by this push:
+        other_ref_sha1s = self._compute_other_ref_sha1s()
+
+        self._old_rev_exclusion_spec = self._compute_rev_exclusion_spec(
+            other_ref_sha1s.union(
+                change.old.sha1
+                for change in self.changes
+                if change.old.type in ['commit', 'tag']
+                )
+            )
+        self._new_rev_exclusion_spec = self._compute_rev_exclusion_spec(
+            other_ref_sha1s.union(
+                change.new.sha1
+                for change in self.changes
+                if change.new.type in ['commit', 'tag']
+                )
+            )
+
+    @classmethod
+    def _sort_key(klass, change):
+        return (klass.SORT_ORDER[change.__class__, change.change_type], change.refname,)
+
+    def _compute_other_ref_sha1s(self):
+        """Return the GitObjects referred to by references unaffected by this push."""
+
+        # The refnames being changed by this push:
+        updated_refs = set(
+            change.refname
+            for change in self.changes
+            )
+
+        # The SHA-1s of commits referred to by all references in this
+        # repository *except* updated_refs:
+        sha1s = set()
+        fmt = (
+            '%(objectname) %(objecttype) %(refname)\n'
+            '%(*objectname) %(*objecttype) %(refname)'
+            )
+        for line in read_git_lines(['for-each-ref', '--format=%s' % (fmt,)]):
+            (sha1, type, name) = line.split(' ', 2)
+            if sha1 and type == 'commit' and name not in updated_refs:
+                sha1s.add(sha1)
+
+        return sha1s
+
+    def _compute_rev_exclusion_spec(self, sha1s):
+        """Return an exclusion specification for 'git rev-list'.
+
+        git_objects is an iterable over GitObject instances.  Return a
+        string that can be passed to the standard input of 'git
+        rev-list --stdin' to exclude all of the commits referred to by
+        git_objects."""
+
+        return ''.join(
+            ['^%s\n' % (sha1,) for sha1 in sorted(sha1s)]
+            )
+
+    def get_new_commits(self, reference_change=None):
+        """Return a list of commits added by this push.
+
+        Return a list of the object names of commits that were added
+        by the part of this push represented by reference_change.  If
+        reference_change is None, then return a list of *all* commits
+        added by this push."""
+
+        if not reference_change:
+            new_revs = sorted(
+                change.new.sha1
+                for change in self.changes
+                if change.new
+                )
+        elif not reference_change.new.commit_sha1:
+            return []
+        else:
+            new_revs = [reference_change.new.commit_sha1]
+
+        cmd = ['rev-list', '--stdin'] + new_revs
+        return read_git_lines(cmd, input=self._old_rev_exclusion_spec)
+
+    def get_discarded_commits(self, reference_change):
+        """Return a list of commits discarded by this push.
+
+        Return a list of the object names of commits that were
+        entirely discarded from the repository by the part of this
+        push represented by reference_change."""
+
+        if not reference_change.old.commit_sha1:
+            return []
+        else:
+            old_revs = [reference_change.old.commit_sha1]
+
+        cmd = ['rev-list', '--stdin'] + old_revs
+        return read_git_lines(cmd, input=self._new_rev_exclusion_spec)
+
+    def send_emails(self, mailer, body_filter=None):
+        """Use send all of the notification emails needed for this push.
+
+        Use send all of the notification emails (including reference
+        change emails and commit emails) needed for this push.  Send
+        the emails using mailer.  If body_filter is not None, then use
+        it to filter the lines that are intended for the email
+        body."""
+
+        # The sha1s of commits that were introduced by this push.
+        # They will be removed from this set as they are processed, to
+        # guarantee that one (and only one) email is generated for
+        # each new commit.
+        unhandled_sha1s = set(self.get_new_commits())
+        for change in self.changes:
+            # Check if we've got anyone to send to
+            if not change.recipients:
+                sys.stderr.write(
+                    '*** no recipients configured so no email will be sent\n'
+                    '*** for %r update %s->%s\n'
+                    % (change.refname, change.old.sha1, change.new.sha1,)
+                    )
+            else:
+                sys.stderr.write('Sending notification emails to: %s\n' % (change.recipients,))
+                mailer.send(change.generate_email(self, body_filter), change.recipients)
+
+            sha1s = []
+            for sha1 in reversed(list(self.get_new_commits(change))):
+                if sha1 in unhandled_sha1s:
+                    sha1s.append(sha1)
+                    unhandled_sha1s.remove(sha1)
+
+            max_emails = change.environment.maxcommitemails
+            if max_emails and len(sha1s) > max_emails:
+                sys.stderr.write(
+                    '*** Too many new commits (%d), not sending commit emails.\n' % len(sha1s)
+                    + '*** Try setting multimailhook.maxCommitEmails to a greater value\n'
+                    + '*** Currently, multimailhook.maxCommitEmails=%d\n' % max_emails
+                    )
+                return
+
+            for (num, sha1) in enumerate(sha1s):
+                rev = Revision(change, GitObject(sha1), num=num+1, tot=len(sha1s))
+                if rev.recipients:
+                    mailer.send(rev.generate_email(self, body_filter), rev.recipients)
+
+        # Consistency check:
+        if unhandled_sha1s:
+            sys.stderr.write(
+                'ERROR: No emails were sent for the following new commits:\n'
+                '    %s\n'
+                % ('\n    '.join(sorted(unhandled_sha1s)),)
+                )
+
+
+def run_as_post_receive_hook(environment, mailer):
+    changes = []
+    for line in sys.stdin:
+        (oldrev, newrev, refname) = line.strip().split(' ', 2)
+        changes.append(
+            ReferenceChange.create(environment, oldrev, newrev, refname)
+            )
+    push = Push(changes)
+    push.send_emails(mailer, body_filter=environment.filter_body)
+
+
+def run_as_update_hook(environment, mailer, refname, oldrev, newrev):
+    changes = [
+        ReferenceChange.create(
+            environment,
+            read_git_output(['rev-parse', '--verify', oldrev]),
+            read_git_output(['rev-parse', '--verify', newrev]),
+            refname,
+            ),
+        ]
+    push = Push(changes)
+    push.send_emails(mailer, body_filter=environment.filter_body)
+
+
+def choose_mailer(config, environment):
+    mailer = config.get('mailer', default='sendmail')
+
+    if mailer == 'smtp':
+        smtpserver = config.get('smtpserver', default='localhost')
+        mailer = SMTPMailer(
+            envelopesender=(environment.get_sender() or environment.get_fromaddr()),
+            smtpserver=smtpserver,
+            )
+    elif mailer == 'sendmail':
+        command = config.get('sendmailcommand')
+        if command:
+            command = shlex.split(command)
+        mailer = SendMailer(command=command, envelopesender=environment.get_sender())
+    else:
+        sys.stderr.write(
+            'fatal: multimailhook.mailer is set to an incorrect value: "%s"\n' % mailer
+            + 'please use one of "smtp" or "sendmail".\n'
+            )
+        sys.exit(1)
+    return mailer
+
+
+KNOWN_ENVIRONMENTS = {
+    'generic' : GenericEnvironmentMixin,
+    'gitolite' : GitoliteEnvironmentMixin,
+    }
+
+
+def choose_environment(config, osenv=None, env=None, recipients=None):
+    if not osenv:
+        osenv = os.environ
+
+    environment_mixins = [
+        ProjectdescEnvironmentMixin,
+        ConfigMaxlinesEnvironmentMixin,
+        ConfigFilterLinesEnvironmentMixin,
+        PusherDomainEnvironmentMixin,
+        ConfigOptionsEnvironmentMixin,
+        ]
+    environment_kw = {
+        'osenv' : osenv,
+        'config' : config,
+        }
+
+    if not env:
+        env = config.get('environment')
+
+    if not env:
+        if 'GL_USER' in osenv and 'GL_REPO' in osenv:
+            env = 'gitolite'
+        else:
+            env = 'generic'
+
+    environment_mixins.append(KNOWN_ENVIRONMENTS[env])
+
+    if recipients:
+        environment_mixins.insert(0, StaticRecipientsEnvironmentMixin)
+        environment_kw['refchange_recipients'] = recipients
+        environment_kw['announce_recipients'] = recipients
+        environment_kw['revision_recipients'] = recipients
+    else:
+        environment_mixins.insert(0, ConfigRecipientsEnvironmentMixin)
+
+    environment_klass = type(
+        'EffectiveEnvironment',
+        tuple(environment_mixins) + (Environment,),
+        {},
+        )
+    return environment_klass(**environment_kw)
+
+
+def main(args):
+    parser = optparse.OptionParser(
+        description=__doc__,
+        usage='%prog [OPTIONS]\n   or: %prog [OPTIONS] REFNAME OLDREV NEWREV',
+        )
+
+    parser.add_option(
+        '--environment', '--env', action='store', type='choice',
+        choices=['generic', 'gitolite'], default=None,
+        help=(
+            'Choose type of environment is in use.  Default is taken from '
+            'multimailhook.environment if set; otherwise "generic".'
+            ),
+        )
+    parser.add_option(
+        '--stdout', action='store_true', default=False,
+        help='Output emails to stdout rather than sending them.',
+        )
+    parser.add_option(
+        '--recipients', action='store', default=None,
+        help='Set list of email recipients for all types of emails.',
+        )
+    parser.add_option(
+        '--show-env', action='store_true', default=False,
+        help=(
+            'Write to stderr the values determined for the environment '
+            '(intended for debugging purposes).'
+            ),
+        )
+
+    (options, args) = parser.parse_args(args)
+
+    config = Config('multimailhook')
+
+    try:
+        environment = choose_environment(
+            config, osenv=os.environ,
+            env=options.environment,
+            recipients=options.recipients,
+            )
+
+        if options.show_env:
+            sys.stderr.write('Environment values:\n')
+            for (k,v) in sorted(environment.get_values().items()):
+                sys.stderr.write('    %s : %r\n' % (k,v))
+            sys.stderr.write('\n')
+
+        if options.stdout:
+            mailer = OutputMailer(sys.stdout)
+        else:
+            mailer = choose_mailer(config, environment)
+
+        # Dual mode: if arguments were specified on the command line, run
+        # like an update hook; otherwise, run as a post-receive hook.
+        if args:
+            if len(args) != 3:
+                parser.error('Need zero or three non-option arguments')
+            (refname, oldrev, newrev) = args
+            run_as_update_hook(environment, mailer, refname, oldrev, newrev)
+        else:
+            run_as_post_receive_hook(environment, mailer)
+    except ConfigurationException, e:
+        sys.exit(str(e))
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])
diff --git a/contrib/hooks/multimail/migrate-mailhook-config b/contrib/hooks/multimail/migrate-mailhook-config
new file mode 100755
index 0000000000..04eeaac413
--- /dev/null
+++ b/contrib/hooks/multimail/migrate-mailhook-config
@@ -0,0 +1,269 @@
+#! /usr/bin/env python2
+
+"""Migrate a post-receive-email configuration to be usable with git_multimail.py.
+
+See README.migrate-from-post-receive-email for more information.
+
+"""
+
+import sys
+import optparse
+
+from git_multimail import CommandError
+from git_multimail import Config
+from git_multimail import read_output
+
+
+OLD_NAMES = [
+    'mailinglist',
+    'announcelist',
+    'envelopesender',
+    'emailprefix',
+    'showrev',
+    'emailmaxlines',
+    'diffopts',
+    ]
+
+NEW_NAMES = [
+    'environment',
+    'reponame',
+    'mailinglist',
+    'refchangelist',
+    'commitlist',
+    'announcelist',
+    'announceshortlog',
+    'envelopesender',
+    'administrator',
+    'emailprefix',
+    'emailmaxlines',
+    'diffopts',
+    'emaildomain',
+    ]
+
+
+INFO = """\
+
+SUCCESS!
+
+Your post-receive-email configuration has been converted to
+git-multimail format.  Please see README and
+README.migrate-from-post-receive-email to learn about other
+git-multimail configuration possibilities.
+
+For example, git-multimail has the following new options with no
+equivalent in post-receive-email.  You might want to read about them
+to see if they would be useful in your situation:
+
+"""
+
+
+def _check_old_config_exists(old):
+    """Check that at least one old configuration value is set."""
+
+    for name in OLD_NAMES:
+        if old.has_key(name):
+            return True
+
+    return False
+
+
+def _check_new_config_clear(new):
+    """Check that none of the new configuration names are set."""
+
+    retval = True
+    for name in NEW_NAMES:
+        if new.has_key(name):
+            if retval:
+                sys.stderr.write('INFO: The following configuration values already exist:\n\n')
+            sys.stderr.write('    "%s.%s"\n' % (new.section, name))
+            retval = False
+
+    return retval
+
+
+def erase_values(config, names):
+    for name in names:
+        if config.has_key(name):
+            try:
+                sys.stderr.write('...unsetting "%s.%s"\n' % (config.section, name))
+                config.unset_all(name)
+            except CommandError:
+                sys.stderr.write(
+                    '\nWARNING: could not unset "%s.%s".  '
+                    'Perhaps it is not set at the --local level?\n\n'
+                    % (config.section, name)
+                    )
+
+
+def is_section_empty(section, local):
+    """Return True iff the specified configuration section is empty.
+
+    Iff local is True, use the --local option when invoking 'git
+    config'."""
+
+    if local:
+        local_option = ['--local']
+    else:
+        local_option = []
+
+    try:
+        read_output(
+            ['git', 'config']
+            + local_option
+            + ['--get-regexp', '^%s\.' % (section,)]
+            )
+    except CommandError, e:
+        if e.retcode == 1:
+            # This means that no settings were found.
+            return True
+        else:
+            raise
+    else:
+        return False
+
+
+def remove_section_if_empty(section):
+    """If the specified configuration section is empty, delete it."""
+
+    try:
+        empty = is_section_empty(section, local=True)
+    except CommandError:
+        # Older versions of git do not support the --local option, so
+        # if the first attempt fails, try without --local.
+        try:
+            empty = is_section_empty(section, local=False)
+        except CommandError:
+            sys.stderr.write(
+                '\nINFO: If configuration section "%s.*" is empty, you might want '
+                'to delete it.\n\n'
+                % (section,)
+                )
+            return
+
+    if empty:
+        sys.stderr.write('...removing section "%s.*"\n' % (section,))
+        read_output(['git', 'config', '--remove-section', section])
+    else:
+        sys.stderr.write(
+            '\nINFO: Configuration section "%s.*" still has contents.  '
+            'It will not be deleted.\n\n'
+            % (section,)
+            )
+
+
+def migrate_config(strict=False, retain=False, overwrite=False):
+    old = Config('hooks')
+    new = Config('multimailhook')
+    if not _check_old_config_exists(old):
+        sys.exit(
+            'Your repository has no post-receive-email configuration.  '
+            'Nothing to do.'
+            )
+    if not _check_new_config_clear(new):
+        if overwrite:
+            sys.stderr.write('\nWARNING: Erasing the above values...\n\n')
+            erase_values(new, NEW_NAMES)
+        else:
+            sys.exit(
+                '\nERROR: Refusing to overwrite existing values.  Use the --overwrite\n'
+                'option to continue anyway.'
+                )
+
+    name = 'showrev'
+    if old.has_key(name):
+        msg = 'git-multimail does not support "%s.%s"' % (old.section, name,)
+        if strict:
+            sys.exit(
+                'ERROR: %s.\n'
+                'Please unset that value then try again, or run without --strict.'
+                % (msg,)
+                )
+        else:
+            sys.stderr.write('\nWARNING: %s (ignoring).\n\n' % (msg,))
+
+    for name in ['mailinglist', 'announcelist']:
+        if old.has_key(name):
+            sys.stderr.write(
+                '...copying "%s.%s" to "%s.%s"\n' % (old.section, name, new.section, name)
+                )
+            new.set_recipients(name, old.get_recipients(name))
+
+    if strict:
+        sys.stderr.write(
+            '...setting "%s.commitlist" to the empty string\n' % (new.section,)
+            )
+        new.set_recipients('commitlist', '')
+        sys.stderr.write(
+            '...setting "%s.announceshortlog" to "true"\n' % (new.section,)
+            )
+        new.set('announceshortlog', 'true')
+
+    for name in ['envelopesender', 'emailmaxlines', 'diffopts']:
+        if old.has_key(name):
+            sys.stderr.write(
+                '...copying "%s.%s" to "%s.%s"\n' % (old.section, name, new.section, name)
+                )
+            new.set(name, old.get(name))
+
+    name = 'emailprefix'
+    if old.has_key(name):
+        sys.stderr.write(
+            '...copying "%s.%s" to "%s.%s"\n' % (old.section, name, new.section, name)
+            )
+        new.set(name, old.get(name))
+    elif strict:
+        sys.stderr.write(
+            '...setting "%s.%s" to "[SCM]" to preserve old subject lines\n'
+            % (new.section, name)
+            )
+        new.set(name, '[SCM]')
+
+    if not retain:
+        erase_values(old, OLD_NAMES)
+        remove_section_if_empty(old.section)
+
+    sys.stderr.write(INFO)
+    for name in NEW_NAMES:
+        if name not in OLD_NAMES:
+            sys.stderr.write('    "%s.%s"\n' % (new.section, name,))
+    sys.stderr.write('\n')
+
+
+def main(args):
+    parser = optparse.OptionParser(
+        description=__doc__,
+        usage='%prog [OPTIONS]',
+        )
+
+    parser.add_option(
+        '--strict', action='store_true', default=False,
+        help=(
+            'Slavishly configure git-multimail as closely as possible to '
+            'the post-receive-email configuration.  Default is to turn '
+            'on some new features that have no equivalent in post-receive-email.'
+            ),
+        )
+    parser.add_option(
+        '--retain', action='store_true', default=False,
+        help=(
+            'Retain the post-receive-email configuration values.  '
+            'Default is to delete them after the new values are set.'
+            ),
+        )
+    parser.add_option(
+        '--overwrite', action='store_true', default=False,
+        help=(
+            'Overwrite any existing git-multimail configuration settings.  '
+            'Default is to abort if such settings already exist.'
+            ),
+        )
+
+    (options, args) = parser.parse_args(args)
+
+    if args:
+        parser.error('Unexpected arguments: %s' % (' '.join(args),))
+
+    migrate_config(strict=options.strict, retain=options.retain, overwrite=options.overwrite)
+
+
+main(sys.argv[1:])
diff --git a/contrib/hooks/multimail/post-receive b/contrib/hooks/multimail/post-receive
new file mode 100755
index 0000000000..93ebb437d1
--- /dev/null
+++ b/contrib/hooks/multimail/post-receive
@@ -0,0 +1,90 @@
+#! /usr/bin/env python2
+
+"""Example post-receive hook based on git-multimail.
+
+This script is a simple example of a post-receive hook implemented
+using git_multimail.py as a Python module.  It is intended to be
+customized before use; see the comments in the script to help you get
+started.
+
+It is possible to use git_multimail.py itself as a post-receive or
+update hook, configured via git config settings and/or command-line
+parameters.  But for more flexibility, it can also be imported as a
+Python module by a custom post-receive script as done here.  The
+latter has the following advantages:
+
+* The tool's behavior can be customized using arbitrary Python code,
+  without having to edit git_multimail.py.
+
+* Configuration settings can be read from other sources; for example,
+  user names and email addresses could be read from LDAP or from a
+  database.  Or the settings can even be hardcoded in the importing
+  Python script, if this is preferred.
+
+This script is a very basic example of how to use git_multimail.py as
+a module.  The comments below explain some of the points at which the
+script's behavior could be changed or customized.
+
+"""
+
+import sys
+import os
+
+# If necessary, add the path to the directory containing
+# git_multimail.py to the Python path as follows.  (This is not
+# necessary if git_multimail.py is in the same directory as this
+# script):
+
+#LIBDIR = 'path/to/directory/containing/module'
+#sys.path.insert(0, LIBDIR)
+
+import git_multimail
+
+
+# It is possible to modify the output templates here; e.g.:
+
+#git_multimail.FOOTER_TEMPLATE = """\
+#
+#-- \n\
+#This email was generated by the wonderful git-multimail tool.
+#"""
+
+
+# Specify which "git config" section contains the configuration for
+# git-multimail:
+config = git_multimail.Config('multimailhook')
+
+
+# Select the type of environment:
+environment = git_multimail.GenericEnvironment(config=config)
+#environment = git_multimail.GitoliteEnvironment(config=config)
+
+
+# Choose the method of sending emails based on the git config:
+mailer = git_multimail.choose_mailer(config, environment)
+
+# Alternatively, you may hardcode the mailer using code like one of
+# the following:
+
+# Use "/usr/sbin/sendmail -t" to send emails.  The envelopesender
+# argument is optional:
+#mailer = git_multimail.SendMailer(
+#    command=['/usr/sbin/sendmail', '-t'],
+#    envelopesender='git-repo@example.com',
+#    )
+
+# Use Python's smtplib to send emails.  Both arguments are required.
+#mailer = git_multimail.SMTPMailer(
+#    envelopesender='git-repo@example.com',
+#    # The smtpserver argument can also include a port number; e.g.,
+#    #     smtpserver='mail.example.com:25'
+#    smtpserver='mail.example.com',
+#    )
+
+# OutputMailer is intended only for testing; it writes the emails to
+# the specified file stream.
+#mailer = git_multimail.OutputMailer(sys.stdout)
+
+
+# Read changes from stdin and send notification emails:
+git_multimail.run_as_post_receive_hook(environment, mailer)