[Mailman-Users] iterative loop

[Web Analysts]

Using mailman 2.1.9 on ubuntu 14.04 using mysql for aliases and mail
accounts. Iy was working fine for a long time then something went awry. Now
I've got an iterative loop and multiple email lists are generating
'Undelivered Mail Returned to Sender' messages. Those message then have the
following email as an attachment:


This is the mail system at host mail.domainname.tld.

I'm sorry to have to inform you that your message could not be delivered to
one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own
text from the attached returned message.

                   The mail system

<|/var/lib/mailman/mail/mailman@ hostname.domainname.tld >: unknown user:
    "|/var/lib/mailman/mail/mailman"


Please advise. Thank you!