Cooking headers

Messages that flow through the global pipeline get their headers ‘cooked’, which basically means that their headers go through several mostly unrelated transformations. Some headers get added, others get changed. Some of these changes depend on mailing list settings and others depend on how the message is getting sent through the system. We’ll take things one-by-one.

>>> mlist = create_list('_xtest@example.com')
>>> mlist.subject_prefix = ''
>>> mlist.include_list_post_header = False
>>> mlist.archive = True

Saving the original sender

Because the original sender headers may get deleted or changed, this handler will place the sender in the message metadata for safe keeping.

>>> msg = message_from_string("""\
... From: aperson@example.com
...
... A message of great import.
... """)
>>> msgdata = {}

>>> from mailman.pipeline.cook_headers import process
>>> process(mlist, msg, msgdata)
>>> print msgdata['original_sender']
aperson@example.com

But if there was no original sender, then the empty string will be saved.

>>> msg = message_from_string("""\
... Subject: No original sender
...
... A message of great import.
... """)
>>> msgdata = {}
>>> process(mlist, msg, msgdata)
>>> print msgdata['original_sender']
<BLANKLINE>

Mailman version header

Mailman will also insert an X-Mailman-Version header...

>>> msg = message_from_string("""\
... From: aperson@example.com
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> from mailman.version import VERSION
>>> msg['x-mailman-version'] == VERSION
True

...but only if one doesn’t already exist.

>>> msg = message_from_string("""\
... From: aperson@example.com
... X-Mailman-Version: 3000
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print msg['x-mailman-version']
3000

Precedence header

Mailman will insert a Precedence header, which is a de-facto standard for telling automatic reply software (e.g. vacation(1)) not to respond to this message.

>>> msg = message_from_string("""\
... From: aperson@example.com
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print msg['precedence']
list

But Mailman will only add that header if the original message doesn’t already have one of them.

>>> msg = message_from_string("""\
... From: aperson@example.com
... Precedence: junk
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print msg['precedence']
junk

RFC 2919 and 2369 headers

This is a helper function for the following section.

>>> def list_headers(msg):
...     print '---start---'
...     # Sort the List-* headers found in the message.  We need to do
...     # this because CookHeaders puts them in a dictionary which does
...     # not have a guaranteed sort order.
...     for header in sorted(msg.keys()):
...         parts = header.lower().split('-')
...         if 'list' not in parts:
...             continue
...         for value in msg.get_all(header):
...             print '%s: %s' % (header, value)
...     print '---end---'

These RFCs define headers for mailing list actions. A mailing list should generally add these headers, but not for messages that aren’t crafted for a specific list (e.g. password reminders in Mailman 2.x).

>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, dict(_nolist=True))
>>> list_headers(msg)
---start---
---end---

Some people don’t like these headers because their mail readers aren’t good about hiding them. A list owner can turn these headers off.

>>> mlist.include_rfc2369_headers = False
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
---end---

But normally, a list will include these headers.

>>> mlist.include_rfc2369_headers = True
>>> mlist.include_list_post_header = True
>>> mlist.preferred_language = 'en'
>>> msg = message_from_string("""\
... From: aperson@example.com
... Message-ID: <12345>
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
List-Archive: <http://lists.example.com/archives/_xtest@example.com>
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Id: <_xtest.example.com>
List-Post: <mailto:_xtest@example.com>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
---end---

If the mailing list has a description, then it is included in the List-Id header.

>>> mlist.description = 'My test mailing list'
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
List-Archive: <http://lists.example.com/archives/_xtest@example.com>
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Id: My test mailing list <_xtest.example.com>
List-Post: <mailto:_xtest@example.com>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
---end---

There are some circumstances when the list administrator wants to explicitly set the List-ID header. Start by creating a new domain.

>>> from mailman.interfaces.domain import IDomainManager
>>> from zope.component import getUtility
>>> domain = getUtility(IDomainManager).add('mail.example.net')
>>> mlist.host_name = 'mail.example.net'

>>> process(mlist, msg, {})
>>> print msg['list-id']
My test mailing list <_xtest.example.com>

>>> mlist.list_id = '_xtest.mail.example.net'
>>> process(mlist, msg, {})
>>> print msg['list-id']
My test mailing list <_xtest.mail.example.net>

>>> mlist.host_name = 'example.com'
>>> mlist.list_id = '_xtest.example.com'

Any existing List-ID headers are removed from the original message.

>>> msg = message_from_string("""\
... From: aperson@example.com
... List-ID: <123.456.789>
...
... """)
>>> process(mlist, msg, {})
>>> sorted(msg.get_all('list-id'))
[u'My test mailing list <_xtest.example.com>']

Administrative messages crafted by Mailman will have a reduced set of headers.

>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, dict(reduced_list_headers=True))
>>> list_headers(msg)
---start---
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Id: My test mailing list <_xtest.example.com>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
X-List-Administrivia: yes
---end---

With the normal set of List-* headers, it’s still possible to suppress the List-Post header, which is reasonable for an announce only mailing list.

>>> mlist.include_list_post_header = False
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
List-Archive: <http://lists.example.com/archives/_xtest@example.com>
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Id: My test mailing list <_xtest.example.com>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
---end---

And if the list isn’t being archived, it makes no sense to add the List-Archive header either.

>>> mlist.include_list_post_header = True
>>> mlist.archive = False
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Id: My test mailing list <_xtest.example.com>
List-Post: <mailto:_xtest@example.com>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
---end---

Archived-At

RFC 5064 (draft) defines a new Archived-At header which contains the url to the individual message in the archives. The stock Pipermail archiver doesn’t support this because the url can’t be calculated until after the message is archived. Because this is done by the archive runner, this information isn’t available to us now.

>>> print msg['archived-at']
None

Personalization

The To field normally contains the list posting address. However when messages are fully personalized, that header will get overwritten with the address of the recipient. The list’s posting address will be added to one of the recipient headers so that users will be able to reply back to the list.

>>> from mailman.interfaces.mailinglist import (
...     Personalization, ReplyToMunging)
>>> mlist.personalize = Personalization.full
>>> mlist.reply_goes_to_list = ReplyToMunging.no_munging
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> print msg.as_string()
From: aperson@example.com
X-BeenThere: _xtest@example.com
X-Mailman-Version: ...
Precedence: list
Cc: My test mailing list <_xtest@example.com>
List-Id: My test mailing list <_xtest.example.com>
List-Unsubscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-leave@example.com>
List-Post: <mailto:_xtest@example.com>
List-Help: <mailto:_xtest-request@example.com?subject=help>
List-Subscribe: <http://lists.example.com/listinfo/_xtest@example.com>,
    <mailto:_xtest-join@example.com>
<BLANKLINE>
<BLANKLINE>

Table Of Contents

Previous topic

Cleansing headers

Next topic

Message decoration

This Page