I have just finished setting up a Postfix mail server on a linux (ubuntu) platform. I have it sending and receiving email and it is not an open relay. It also supports secure smtp and imap.
Now this is a pretty beginner question but should I be leaving port 25 open? (since secure smtp is preferred). if so then why?
Also what about port 587?
Also should I require any authentication on either of these ports?
Please excuse my ignorance in this area :P