[Mailman-Users] message to list does not get forwarded to all list members

[Peter Wetz]

Currently I experience the following issue on my list: If one specific
subscriber posts a message to the list, it does not get forwarded to all
list members. However, some (at least one) receives his messages. But most,
don't receive his message. The message also shows up properly in the list
archive.

What is the problem? How can I debug this? Why does the message not get
through to all list members?

The domain of the source mail is yahoo.com

Thanks and best,
Peter