Setting up a new CentOS 6 server with Plesk 10.4.4 using Postfix, I am unable to send emails from any user account on port 25, 465, or 587 without having SSL enabled. If I check to use SSL in Apple Mail, on iPhone, or in Outlook, everything works fine. Without, emails will not send and I get errors saying the SMTP server connection failed. I'm using apf and have the ports enabled, and have also disabled the firewall during testing and still have no luck.
On my old CentOS 5 box with Plesk 10.1 this isn't a problem, and I have all users sending email through 587 with user/pass authentication due to most ISPs blocking access to 25. I've seen plenty of articles on what to do if you can send without SSL but not with, however I'm not finding much on the other way around. Any help would be much appreciated!