How to Handle Bounce Error Messages in Mailman


Learn about bounce error messages and how to adjust your settings accordingly.


Critical Concepts

When email to a subscriber is bouncing, Mailman tries to interpret the bounced message and act accordingly. When a bounced message is received, Mailman attempts to extract two pieces of information from the message:

If no email address for the subscriber can be extracted from the bounce, then the bounce is usually discarded.

The severity of the problem can be labeled as either hard (meaning a fatal error) or soft (meaning a temporary error occurred). When in doubt, a hard severity is assigned.

Each subscriber is assigned a bounce score and every time Mailman encounters a bounce from this member, the score goes up. Hard bounces increase the score by 1, while soft bounces increase the score by 0.5. However, bounce scores are only increased once per day so even if ten hard bounces are received for the same subscriber in one day, that subscriber’s score will increase by only 1 for that day.


Steps to Take

To adjust settings regarding bounced messages:

  1. Log in to the list's administration page: with your Active Directory username and password (replace ListName with the actual name of your list. The final character is a lowercase letter 'L' for 'list.')
  2. Go to Bounce Processing to adjust these bounce settings:
    • bounce score threshold: When a member’s bounce score exceeds the list’s bounce score threshold, the subscriber’s subscription is automatically disabled. Once disabled, the subscriber will not receive any postings from the list until their membership is explicitly re-enabled (either by them or the list owner). However, they will receive occasional reminders that their membership has been disabled, with information about how to re-enable it.
    • bounce_info_stale_after: After a certain period of time during which no bounces from the subscriber’s address are received, the bounce information is considered stale and discarded.
      Note: By adjusting the bounce_score_threshold and bounce_info_stale_after setting, you can control how quickly members with bouncing email are disabled. You should set both of these to the frequency and traffic volume of your list.
    • bounce_you_are_disabled_warnings: Control the number of reminders the subscribers will receive.
    • bounce_you_are_disabled_warnings_interval: Control how frequently reminders are sent.
  3. When finished, Submit Your Changes.


If Mailman cannot interpret a particular bounced message error, it will be forwarded on to the list owner. Some of the message content requires an expert to interpret it. You can ignore much of the message as long as you know what’s important to focus on. Look for a line that says something like:

Mail could not be delivered to: followed by an email address.

If you find such a line, you know whose email is bouncing and you may even know why (it will sometimes say the reason right after the email address).

What you’ll need to do is decide whether the reason is temporary or permanent. Sometimes the best way to make that decision is to wait a few days or a week and see if you are still receiving error messages from the same subscriber. If so, you’ll probably want to remove that subscriber from your list.

If all else fails and you can’t figure out the errors you’re getting, don’t hesitate to seek assistance by forwarding a copy of the error message to

If you still have questions or need additional assistance, please submit a ticket or call the ITS Service Desk at (858) 246-4357