This is going to be a lengthy explanation, as I've spent a bit of time 
troubleshooting this issue.
I am running Mailman 2.1.20 as part of a server running WHM/cpanel.
The MTA is Exim.
The MTA was configured to reject DKIM failures.
The domain was configured to sign outgoing messages with DKIM.
We noticed that when messages were posted by gmail users, they would appear in 
the list archives but they would not be delivered to any list members. Posts by 
other domains such as my custom office 365 domain worked fine and were 
delivered to everyone including gmail users.
Of course my first stop was the logs, and I saw entries like this in the 
smtp-failure log:
Aug 11 22:06:50 2015 (3128) SMTP session failure: 550, DKIM: encountered the 
following problem validating gmail.com:
signature_incorrect, msgid: 
<CAHtjcYNyqX8Na44GC9GKUsS=2FbS=hd1ofu3gqcjkzuromw...@mail.gmail.com>
Aug 11 22:06:50 2015 (3128) SMTP session failure: 550, DKIM: encountered the 
following problem validating gmail.com:
signature_incorrect, msgid: 
<CAHtjcYNyqX8Na44GC9GKUsS=2FbS=hd1ofu3gqcjkzuromw...@mail.gmail.com>
Thinking that our signing of DKIM was causing issues, I shut that off. That 
didn't change anything.
So, next, thinking that the DMARC issues that have been plaguing the internet 
lately were to blame, I tried changing the DMARC_Moderation setting to munge. 
This failed to change the situation as well.
I then attempted to set this setting to wrap message, which again did not fix 
the issue.
At this point, I moved on to the from as list global setting, and tried munge 
here as well. This didn't work.
Last, I tried wrap message, which did seem to work. Given the functionality 
issues this created, however, I decided to keep investigating.
It was at this point that I decided to turn off DKIM failure rejection. I 
initially dismissed this course of action because I felt that changing the from 
as list setting to munge should have prevented this from becoming an issue. 
Since the initial posts were making it to the web-based archives I figured the 
gmail signature was fine.
I'm at a loss of where to go from here. I would like to still reject DKIM 
failures, but my mailing lists need to work properly as well. Does anyone have 
any suggestions or ideas on why the Munge setting didn't seem to have an impact?




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