I think https://forum.cloudron.io/topic/1660/sympa-mailing-list and https://forum.cloudron.io/topic/6776/mailing-list-feature-basic-moderation are the relevant threads.
@andrewwri maybe you can leave a note in the sympa thread as to how you installed sympa and how you are maintaining it. Maybe some notes on your current set up will also help (what is the email server? how is it interfacing with the email server etc). thanks!