Enabling submission port support for Postfix is really easy. To have postfix listen on both 25 and 587, be sure that the line starting with submission is uncommented in /etc/postfix/master.cf:
smtp inet n - n - - smtpd submission inet n - n - - smtpd
I think you mean: /etc/postfix/master.cf (not main.cf)
@Trashman - Thanks for spotting the error! I've corrected it in the post.
And if your home machine is running linux, you can test your mail server's new config by running the 'swaks' command:
swaks --from me@example.tld --to my-offsite-box@example2.tld --server my-mail-server.example.tld -a -au my-username -ap my-password -tls --port 587
Yeah, the mix of single-dash and multiple-dash parameters is intentional. Swaks has funny arguments.
If you have never playes with swaks, learn it. Especially if you're a mail admin. Awesome tool.
Butbutbut doesn't :587's RFC *REQUIRE* authentication (i.e. it should not allow delivery even to local users without auth)? It shouldn't be a plain "copy" of :25.