Dedicated port 25 for communication between smtp servers and reserve port 587 for Message User Agent (MUA) where you can force TLS or not, that is not possible on smtp port or also apply other rules for smtp client.
http://www.ietf.org/rfc/rfc2476.txt : ... 3.1. Submission Identification Port 587 is reserved for email message submission as specified in this document. Messages received on this port are defined to be submissions. The protocol used is ESMTP [SMTP-MTA, ESMTP], with additional restrictions as specified here. 2008/9/25 Jimmy Spam <[EMAIL PROTECTED]> > Why I should use this port? What is the goal of his use? > > > ______________________________________________________________________ > Correo gratis de Pobladores.com > Ahora con 25MB de capacidad. > http://www.pobladores.com/services/webmail >
