If you provider blocks SMTP 25 port you can use the submission port. Plesk 8 comes with a submission service definition. You don’t need to define a new service. You only need to check the “Enable the Message Submission” option , on the Plesk page Server > Mail > Preferences.

I am working on a KVM based virtualized environment.  All my virtual machines are sitting behind a virtual firewall appliance. Here comes the challenge. I need to identify and open up required ports for each individual appliance. What are the ports a mailserver would need? Here is the list of ports you need to open [...]