Thank you for taking the time to file a bug report. Checking the mailman package in Ubuntu Focal I see the logrotate file installed by this package contains some postrotate scripts that might be setting back the ownership to list:list. Take a look at /etc/logrotate.d/mailman and try to make the appropriate changes.
Since it seems likely to me that this is a local configuration problem, rather than a bug in Ubuntu, I am marking this bug as 'Incomplete'. However, if you believe that this is really a bug in Ubuntu, then we would be grateful if you would provide a more complete description of the problem with steps to reproduce, explain why you believe this is a bug in Ubuntu rather than a problem specific to your system, and then change the bug status back to "New". For local configuration issues, you can find assistance here: http://www.ubuntu.com/support/community ** Changed in: mailman (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1917336 Title: Mailman does not honour MAILMAN_USER on startup To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mailman/+bug/1917336/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs