certuspersonality wrote:

I have sent a email message to an email list of which I am the administrator and also on the member list, received the email requesting approval for publication, gave that approval, and then the email message was sent to me (info@certuspersonality.com) as the original supplier of the message, the number of times that equals the number of members in the email list. It did not go to the list members (except for me).

Which setting do I probably have wrong in Mailman?

It doesn't seem to me that this is a Mailman issue. My best guess based on the limited information is there is some issue with your MTA and/or DNS configuration. It seems that mailman sent the message to the list members, but the MTA couldn't deliver it so it bounced or forwarded those undeliverable messages back to you.

To say anything more, we'd need to see Mailman's 'smtp', 'smtp-failure' and 'bounce' logs, and the MTA's logs showing what it did with those messages.