If you're using Exim 3, you'll need to add the following director to your config file (directors go between the second and third ``end'' lines). Also, don't forget that order matters - e.g. you can make Mailman lists take precedence over system aliases by putting this director in front of your aliasfile director, or vice-versa.
# Handle all addresses related to a list 'foo': the posting address. # Automatically detects list existence by looking # for lists/$local_part/config.pck under MAILMAN_HOME. mailman_director: driver = smartuser require_files = MAILMAN_HOME/lists/$local_part/config.pck suffix_optional suffix = -bounces : -bounces+* : \ -confirm+* : -join : -leave : \ -owner : -request : -admin transport = mailman_transport