How do I enable port 587 (submission) in Postfix?

To enable port 587, edit the file /etc/postfix/master.cf and remove the # in front of the following line:

#submission inet n – n – – smtpd

so that it looks like this:

submission inet n – n – – smtpd

and restart postfix

Also be sure to open port 587 on your firewall.