RFC 2919 and 2369 headers

RFC 2919 and RFC 2369 define headers for mailing list actions. These headers generally start with the List- prefix.

>>> from mailman.app.lifecycle import create_list
>>> mlist = create_list('test@example.com')
>>> mlist.preferred_language = 'en'
>>> from mailman.interfaces.archiver import ArchivePolicy
>>> mlist.archive_policy = ArchivePolicy.never

This is a helper function for the following section.

>>> def list_headers(msg, only=None):
...     if isinstance(only, str):
...         only = (only.lower(),)
...     elif only is None:
...         only = set(header.lower() for header in msg.keys()
...                    if header.lower().startswith('list-'))
...         only.add('archived-at')
...     else:
...         only = set(header.lower() for header in only)
...     print('---start---')
...     for header in sorted(only):
...         for value in sorted(msg.get_all(header, ())):
...             print('%s: %s' % (header, value))
...     print('---end---')

The rfc-2369 handler adds the List- headers. List-Id is always added.

>>> from mailman.handlers.rfc_2369 import process
>>> from mailman.testing.helpers import (specialized_message_from_string
...   as message_from_string)
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg, 'list-id')
---start---
list-id: <test.example.com>
---end---

Fewer headers

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---

Messages which Mailman generates itself, such as user or owner notifications, have a reduced set of List- headers. Specifically, there is no List-Post, List-Archive or Archived-At header. ..

>>> mlist.include_rfc2369_headers = True
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)

>>> process(mlist, msg, dict(reduced_list_headers=True))
>>> list_headers(msg)
---start---
list-help: <mailto:test-request@example.com?subject=help>
list-id: <test.example.com>
list-owner: <mailto:test-owner@example.com>
list-subscribe: <mailto:test-join@example.com>
list-unsubscribe: <mailto:test-leave@example.com>
---end---

List-Post header

Discussion lists, to which any subscriber can post, also have a List-Post header which contains the mailto: URL used to send messages to the list.

>>> mlist.include_rfc2369_headers = True
>>> mlist.allow_list_posts = True
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
list-help: <mailto:test-request@example.com?subject=help>
list-id: <test.example.com>
list-owner: <mailto:test-owner@example.com>
list-post: <mailto:test@example.com>
list-subscribe: <mailto:test-join@example.com>
list-unsubscribe: <mailto:test-leave@example.com>
---end---

Some mailing lists are announce, or one-way lists, not discussion lists. Because the general membership cannot post to these mailing lists, the list owner can set a flag which adds a special List-Post header value, according to RFC 2369.

>>> mlist.allow_list_posts = False
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
list-help: <mailto:test-request@example.com?subject=help>
list-id: <test.example.com>
list-owner: <mailto:test-owner@example.com>
list-post: NO
list-subscribe: <mailto:test-join@example.com>
list-unsubscribe: <mailto:test-leave@example.com>
---end---

List-Id header

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

>>> mlist.allow_list_posts = True
>>> mlist.description = 'My test mailing list'
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> list_headers(msg)
---start---
list-help: <mailto:test-request@example.com?subject=help>
list-id: My test mailing list <test.example.com>
list-owner: <mailto:test-owner@example.com>
list-post: <mailto:test@example.com>
list-subscribe: <mailto:test-join@example.com>
list-unsubscribe: <mailto:test-leave@example.com>
---end---

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, {})
>>> list_headers(msg, only='list-id')
---start---
list-id: My test mailing list <test.example.com>
---end---

Archive headers

When the mailing list is configured to enable archiving, List-Archive headers will be added for each web accessible archiver that is enabled.

RFC 5064 defines the Archived-At header which contains the url to the individual message in the archives. Archivers which don’t support pre-calculation of the archive url cannot add the Archived-At header. However, other archivers can calculate the url, and do add this header.

If the mailing list isn’t being archived, neither the List-Archive nor Archived-At headers will be added.