[Mailman-Users] Messages approved never show up on list

[Doug Gaff]

I'm trying to track down a problem related to message from one particular emailer not showing up on a list.

This person is not subscribed to the list. They send a message, and the moderator approves the message, but it never shows up on the list.

Adding the person as an approved sender also has no effect. This has happened for multiple lists with this particular person. 

Can I get some clues where to look to start diagnosing the problem?