Thomas Stein writes:
Thanks for your answer. So the the file in queue/shunt contains information too? I will have a look.
The file in queue/shunt is the message plus some Mailman metadata, as a Python pickle. You can find out what is in it using "bin/mailman.py qfile", but probably the log and traceback will tell you (or us) everything needed to fix the problem.
If it's a Mailman bug (somewhat unlikely), we send you a patch and you use "bin/mailman.py unshunt" to reinject the message into the mail system via Mailman. If it's a nonconforming mail message (somewhat more likely -- typically this happens when you have raw UTF-8 or other 8-bit characters in the message header), then the easiest thing to do is to edit a saved copy of the message and resend from your mail client. (It's theoretically possible to edit the pickle and use "unshunt", but Mailman currently does not provide that feature.)