Gary Holman writes:

I have seen a few messages on this list regarding handling 'out of office' auto-replies.  However I do not see a final resolution.

This problem is as hard as spam. There won't be a final resolution as long as people use out-of-office auto-replies. They're all different.

If you are using a spam filter, I would suggest adding the offender's out of office message (or at least the spike protein :-) to your filter's body text blacklist.

What is the best practice to filter auto-replies to list: header filter or postfix milter-reject or something else?

You write "auto-replies" below. Set the subscriber to no-mail, or unsubscribe them for a second offense. Remind them that we put a huge amount of effort into creating and maintaining Postorius to make that as convenient as possible, and we at Mailman are "shock, SHOCKED, I tell you" that this courtesy was neglected. :-)

We are running dockerized Mailman 3 version 1.3.4.  A list user auto-replied their vacation message to list and then the listserv

"listserv" is a trademark. Please don't use it to refer to Mailman.

created a chain-reaction of continuously replying to auto-replies by that user.

What do you mean by "chain reaction"? Other subscribers replying to the "out of office" message, or an auto-reply from the Mailman server?

 > There isn't really a good header option to filter

from, as the subject seems to be randomized.

Vacation programs conforming to

https://tools.ietf.org/html/rfc3834 https://tools.ietf.org/html/rfc5230

should provide some header fields to filter on.

HTH, Steve