[exim] Exim and Mailman list delivery

Hello,

We have a small list of around 40 members that we have just transferred to
Mailman/Exim, both the latest version.

If a member sends to the list, only about 23 or so of the messages are being
delivered. The other 17 messages, the same 17 message each time are sitting
in the Exim mail queue and do not want to be delivered. All of these
addresses are reachable including mine as used for this list.

I would be most grateful for a solution to this issue.

Thank you.

Regards,

Adrian.