Campus Mailing Lists, List rejects owner's messages
List owners are not automatically added to the subscribers list. If an owner wants to post to a list or receive that list's messages, they should also add their email address as a subscriber.
The "Who can send messages (send)" setting, which can be found in the "Sending/receiving setup" section of a list's Admin view under Edit List Config, determines who can send messages to a mail list. There are many options a privileged list owner can choose.
For more documentation of these features, see Sending/receiving setup in the SYMPA User Guide on the Illinois Wiki.