Plesk 12 smtp differences? (Firewall)

[kpmedia]

SMTP (submission port) server
SMTP (mail sending) server

- Does one accept the mail on port 25?
- While the other only controls/allows smtp logins?

If so, which is which?

If not correct, then what are the differences?

 

[IgorG]

To protect your server against unauthorized mail relaying or injection of unsolicited bulk mail and allow your customers to send email messages through the port 587 you may use submission.