[Mailman-Developers] Fixing DMARC problems with .invalid munge

[Stephen J. Turnbull]

Bob Puff writes:

 > So guys... Is there a simple little hack we can do within MM 2.1 to
 > try to mitigate this issue, by adding .invalid or some other
 > extension?  I've got a few lists that are getting to the point
 > where MM sends the probe email, and then figures it is not a
 > bouncing address, but a lot of emails are not being delivered.

In Mailman 2.1.16 and later, you don't need a "hack", just to set the
appropriate options[1], and as of 2.1.18-1 Mailman 2 provides four
options (munging "From" to the list-post address and Reply-To to
poster, or wrapping the whole post in a MIME part of a message "From"
the list-post address, with the option of applying the chosem
transformation either to all posts or just to those publishing a DMARC
p=reject policy).

All variants are known to be effective in getting past p=reject.  What
are your other requirements?  Also, is it possible that the problem is
not due to DMARC p=reject, but a different issue that arose at this
time by coincidence?



Footnotes: 
[1]  In Mailman 2.1.16 you also need to enable the options in
mm_cfg.py, but in later versions the DMARC mitigation options are
available to each list individually.  Checking for p=reject requires
installing dnspython, a Python package not part of Mailman or the
Python standard library.