I guess Zentyal will do something with an interface for this.
Guess the user manager will have this included.
For now its a matter of adding them to /etc/fetchmailrc
Its split over a few posts.
https://forum.zentyal.org/index.php/topic,22602.msg86913.html#msg86913The manner that you run fetchmail
fetchmail -F -K -L /var/log/fetchmail
-K - Delete retrieved messages from the remote mailserver. This option forces retrieved mail to be deleted
-L - Specify the log file to which fetchmail should log to
-F - Delete old (previously retrieved) messages from the mailserver before retrieving new messages
Or in the global section of fetchmailrc
nofetchall: Retrieve only new messages (default). If nothing else is specified (e.g. fetchall, keep), this means nofetchall.
fetchall: Fetch all messages whether seen or not.
keep: Don't delete seen messages from server.
nokeep: Delete seen messages from server
sudo man fetchmail will give exacts for the specific version.
Its a pain at the moment but if you need it desparately you will have to do something like in the forum link.