[Mailman-Users] Very strange issue With Mailman + Exchange(?)

[Bruce Johnson]

I am not sure how to figure this out.

Lengthy explanation:

Internally in our Exchange server, that address is a distribution group whose only member is the actual <list-name>@lists.pharmacy.arizona.edu, because the Mailman server is not our mail server. (we have a mildly complicated setup: hybrid OnPrem and O365 exchange + Barracuda spam appliance in front of all of it, which is our actual SMTP server.  

Outgoing email from the list server bypasses Exchange and is sent directly to the Barracuda SMTP server.

For two users and ONLY these two users, somewhere between them and mailman and back, the Mailman list is being expanded to put all the members of the list on the CC line. It then gets held for approval with a ’too many addresses’ message.

I have watched them send an email to the affected list; the list address is NOT in their local address cache, and they are NOT entering any other addresses in the email other than the list address. The only address that appears on the email in their Sent folder is the list address.

Other users in our organization can send to these same lists without this happening. In fact one of the affected users can send to *other* lists on our server with no problems. These are two different lists.

I don’t know that this is specifically a Mailman problem (because it’s only happening with specific users) but I cannot see how  list members are getting stuffed on the CC line otherwise; because Exchange only knows the list address, not the members; only Mailman does.

TLDR: Somehow the all the list addresses are getting stuck onto the list message which then holds it for approval for ’too many addresses’.

-- 
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs