[Mailman-Users] Subscribe OK/ Doesn't Post [Imap-specific]

[Karl R. Balsmeier]

I have a unique problem.  Users operating squirrelmail[via imap] can
subscribe to a list.  But cannot post to it.

They see the traffic, but when responding to a post, the replies never
make it to the list.

The same user can switch to Eudora/Ximian/Kmail[pop3d] and respond to a
post, and see their reply, it makes it to the list just fine.

I've read the logs in mailman, thinking smtp-failures log would have some
answers, none found there or the other logs.  I have also monitored
traffic with my recv'ing MTA, it detects no mails coming from the web
mail/squirrelmail submissions, but sees the complete pop3 sessions just
fine.

/etc/aliases looks fine:
stupid-pet-tricks1: postmaster

Any ideas on which logs I could trace an error out?  It seems unique to
imap clients, does anyone using Exim as their MM MTA suggest a look at
transports/directors instead of Mailman itself?

-krb