3.24. Tracking down elusive subscriber bounces

Some bounce messages returned to Mailman lists as a result of the lists mailing out to its subscribers do not correlate with the known subscribers to the list. These bounce messages refer to mail addresses which are not subscribers.

One possible cause of these bounce notices is the rewriting of mail aliases subscribed to the list, to which mail has been sent by the list, by some MTA handling that outgoing mail.

For example, when someone leaves a job, arrangements may be made for their email alias to be rewritten to some other mail alias. Or arrangements may be made for copies of someone's email to be directed to a work colleague.

Problems arise if the mail address following rewriting is then undeliverable. The bounce message that is generated by the MTA that fails the delivery refers to the rewritten mail address not the original mail address to which Mailman sent the mail. As a consquence, unless the return path to Mailman has been VERP'ed, Mailman cannot correlate the bounce message with any of the list subscribers and can do no more than log the problem in its bounce log.

See So what is this VERP stuff for information about VERP if you are not familiar with it.

The source and cause of these bounces can be a real pain to track down.

One approach you can use, with MM 2.1.x, to track down elusive bounces is to:

1. check that your site admin has configured Mailman so that you can enable personalization for a list and that personalized mail is VERP'ed. If they have not then the technique described below will not work.

2. temporarily enable personalization and VERP for a list with bounce problem.

3. set a maximum bounce score < 1.0 for the list.

4. ensure the list is configured to notify the list owner when bounces cause unsubscribe.

5. send a test message to the list.

6. see what the VERP'ed return addresses are on the bounce notifications of the users unsubscribed because of bounces.

If the address in the VERP'ed return path is not the same as the email address referred to by the MTA generating the bounce then it says that the problem discussed above has been the likely cause of your elusive bounces problem.

btw: Do not forget to disable personalization and VERP for the list unless you can affored the extra resource use needed to support continued use of these features.

Without VERP there is no simple answer to tracking this sort of problem down with MM 2.0.x or 2.1.x

Converted from the Mailman FAQ Wizard

This is one of many Frequently Asked Questions.