smtp uses port 25
the first URL is old but it does help explain:
Might also read:
Suggest installing something like pine/alpine to be able to test sending mail from Moodle server operating system (also handy if an account is setup to rec. notifications, etc. from Moodle).
And a comment/thought about local firewall ... what would protect the server from an inside attack ... either un-intentional (workstation contracted a worm) or intentional?
'spirit of sharing', Ken