How do I configure Mailman to use a remote SMTP server?
A remote SMTP server can be configured in
/usr/lib/mailman/Mailman/Defaults.py using the following directives:
# SMTP host and port, when DELIVERY\\_MODULE is 'SMTPDirect'. Make sure the
# host exists and is resolvable (i.e., if it's the default of "localhost" be
# sure there's a localhost entry in your /etc/hosts file!)
SMTPHOST = 'example.com'
SMTPPORT = 25
Mailman hasn't any ability to authorize itself on mail servers, so the server IP should be white listed on the remote mail server.