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.

>>> from mailman.app.lifecycle import create_list
>>> mlist = create_list('test@example.com')
>>> mlist.subject_prefix = ''

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.

>>> from mailman.testing.helpers import (specialized_message_from_string
...   as message_from_string)
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... A message of great import.
... """)
>>> msgdata = {}

>>> from mailman.handlers.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'])

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

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
>>> mlist.description = 'My test mailing list'
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... """)
>>> process(mlist, msg, {})
>>> print(msg.as_string())
From: aperson@example.com
X-Mailman-Version: ...
Precedence: list
Cc: My test mailing list <test@example.com>