[Bug 1312970] [NEW] DMARC munge action breaks CC: header with full personalization

[Robert Mathews]

Public bug reported:

If you use full personalization, the resulting headers on a message
usually look like:

From: Sender <sender at sender.tld>
To: Recipient <recipient at recipient.tld>
Cc: list at list.tld

Note the "Cc:" (added by Mailman/Handlers/CookHeaders.py beginning at
line 191). The presence of the Cc: header makes "Reply to All" and
"Reply to List" appear in many mail clients.

If a DMARC munge happens, Mailman/HandlersModerate.py does this at line
61:

msgdata['from_is_list'] = 1

However, CookHeaders.py at line 202 later notices that and fails to add
the Cc: header because of it.

Because of this, the headers of a munged message, for example, will look
like:

From: Sender via list <list at list.tld>
Reply-To: Sender <sender at sender.tld>
To: Recipient <recipient at recipient.tld>

There is no "Cc:" header present at all, and popular clients like Gmail
don't offer recipients a "Reply to All" choice for DMARC-munged
messages.

It seems that when using full personalization, the Cc: header should
appear whether or not the From and Reply-To were munged due to DMARC.

(I have manually verified that if the Cc: header was present -- that is,
if the munged headers looked like this:

From: Sender via list <list at list.tld>
Reply-To: Sender <sender at sender.tld>
To: Recipient <recipient at recipient.tld>
Cc: list at list.tld

... then Gmail would correctly offer both "Reply" and "Reply to All"
options and send them to the right places.)

** Affects: mailman
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1312970

Title:
  DMARC munge action breaks CC: header with full personalization

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