After reading several complaints regarding mailman, and messages being stuck in the exim queue, I did a little bit of research and found some interesting tweaks, that have helped my servers overall performance. 1st, you must understand that it is NOT mailman that is causing the messages to not be delivered.. mailman simply creates the messages, and passes it to Exim. It is EXIM that handles the delivery of the messages. Most of what I am about to say comes straight from the exim mailing list: http://www.exim.org/mailman/htdig/exim-users/Week-of-Mon-20021014/044956.html Add the following to your EXIM MAIN CONFIGURATION: and running exim's queuerunner in small cycles (exim -q1m or -q2m). Mailman will send as many MAIL FROM/RCPT TO as it needs. It may result in more than 10 or 100 messages sent in one connection, which will exceed the default value of Exim's smtp_accept_queue_per_connection This is bad because it will cause Exim to switch into queue mode and severely delay delivery of your list messages. The way to fix this is to set mailman's SMTP_MAX_SESSIONS_PER_CONNECTION (in ~mailman/Mailman/mm_cfg.py) to a smaller value than Exim's smtp_accept_queue_per_connection Mailman should ignore Exim delay warning messages, even though Exim should never send this to list messages. Mailman 2.1's general bounce detection and VERP support should greatly improve the bounce detector's hit rates. List existence is determined by the existence of a config.pck file for a list. If you delete lists by foul means, be aware of this. If you are getting Exim or Mailman complaining about user ids when you send mail to a list, check that the MAILMAN_UID and MAILMAN_GID match those of Mailman itself (i.e. what were used in the configure script). Also make sure you do not have aliases in the main alias file for the list.