Matthew A. Marshall wrote:

We have a mailman server which sits on ncep.noaa.gov domain. However, we are advertising the lists as listname@noaa.gov. When an email is sent to listname-request@noaa.gov requesting addition to the list, the message is received by the mailman server. However, it is not processed. If the message is sent to listname-request@ncep.noaa.gov, the message is received by the mailman server and processed.

Please provide more details. How is the message to @noaa.gov "not processed"? Does it make it as far as Mailman? (If not, then it sounds like your mail server is only honoring the Mailman list aliases for the @ncep.noaa.gov hostname.) Which of the names did you use for host_name (AKA Host name this list prefers for email)?

I think I have narrowed it down to how mailman reads message-IDs.

I don't think so. The Message-ID is generated by the sender's client.