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

[Mark Sapiro]

On 4/27/20 11:21 AM, Bruce Johnson wrote:
> I am not sure how to figure this out.
> 
> Lengthy explanation:
> 
> 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.
...
> TLDR: Somehow the all the list addresses are getting stuck onto the list message which then holds it for approval for ’too many addresses’.


I'm really guessing here, but I suspect that the list is not VERPing or
personalizing delivery and the default setting for SMTP_MAX_RCPTS is not
overridden with a small number.

In this case Mailman will send the outgoing message in only a few SMTP
transactions with lots of recipients each. In fact, if this is and
internal list and all the recipients are all in the same TLD, Mailman
will send to all the recipients in one transaction with multiple RCPT TO
commands. I.e., the envelope recipients for the message will be the
whole list, at least if there are fewer than 500 members.

Some MUAs will add the envelope recipients to an X-Apparently-To: header
and I wouldn't put it past Exchange to put them in Cc: even though this
could effectively break Bcc:.

All that notwithstanding, this is the outgoing message, and IIUC the
message never gets posted to the list, unless there's some convoluted
process which reflects the outgoing message back to the list.

I would start by examining the Received: chain in the headers of the
held message to see where it's been.

-- 
Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan