[Mailman-Users] Emails (Of a specific Subject/From type) Vanishing between Submission by Postfix and Posting to a Mailman List

[Traiano Welcome]

Hi List

I have a very strange issue where emails from (only) a particular sender, with a particular subject to a particular list "vanish" once the mta (Postfix) has handed it off to the mailman post command. For example:

Mail handed off from postfix to mailman:

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Feb 17 10:34:44 listserver postfix/smtpd[5221]: DB3EC7EA7A: client=mx01.mtnbusiness.co.za[xx.yy.zz.oo]
Feb 17 10:34:44 listserver postfix/cleanup[4002]: DB3EC7EA7A: message-id=<>
Feb 17 10:34:44 listserver postfix/qmgr[396]: DB3EC7EA7A: from=<support at co.za>, size=12244, nrcpt=2 (queue active)
Feb 17 10:34:44 listserver postfix/local[4998]: DB3EC7EA7A: to=<monkeynuts at listeserver.mtnbusiness.co.za>, relay=local, delay=0.09, delays=0.01/0/0/0.08, dsn=2.0.0, status=sent (delivered to command: /usr/local/mailman/mail/mailman post monkeynuts)
Feb 17 10:34:44 listserver postfix/qmgr[396]: DB3EC7EA7A: removed
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When I look for this mail logged in the post log, I see nothing at all. Next, I create a wrapper script to  grab the mail from the mta when handed off to mailman and the email out to a debug file, just to confirm that  the mail is in fact being handed off to the mailman post command:

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/usr/local/mailman/mail/mailman-wrapper.pl
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This script takes the mail and dumps it into a temp file.

So, when a mail from the sender in question is sent, it's spooled to  a temp file, confirming that the MTA is successfully posting mails to mailman. However I cannot find how to debug  this to a deeper level in order to figure out exactly where and why this mail is not getting posted to the list. I'd like to be able to maybe increase the mailman log level to "verbose debug" but I can't find such an option. Any other means of tracking exactly how a message is getting treated after the post set would be useful.

I tried checking for debug switches on the binary "/usr/local/mailman/mail/mailman" so that I could perhaps modify the post command to be more verbose, but I can't seem to find documentation on any useful flags.
(Note that mails from other senders are posted and distributed correctly)

Please could someone point me in the right direction w.r.t debugging issues of this type ?

Many thanks in advance,
Traiano Welcome