By default, the standard SMTP port (25) is for mail transfer only. Mail relay for submissions from external networks is disabled and authentication is disabled. By default, the standard SMTP submit port (587) is for mail submission and requires authenticated SMTP. As many mail user agents still use port 25 for submission by default it might be useful to enable SMTP authentication on port 25 for those clients.
By default, users need not submit a password when they connect to the SMTP service of Messaging Server to send a message. You can, however, enable password login to SMTP in order to enable authenticated SMTP.
Authenticated SMTP (also referred to as SMTP AUTH) is an extension to the SMTP protocol. Authenticated SMTP allows clients to authenticate to the server. The authentication accompanies the message. The primary use of authenticated SMTP is to enable local users who are not in their office to submit mail without creating an open relay that others could abuse. The AUTH command is used by the client to authenticate to the server.
Authenticated SMTP provides security in sending messages with the SMTP protocol. To use authenticated SMTP, you do not need to deploy a certificate-based infrastructure. (Certificates authentication is described in Certificate-based Authentication with Secure Sockets Layer (SSL).)
If you require SMTP AUTH for mail submission, turn on appropriate logging, so any mail abuse can be traced.
For more information on authenticated SMTP, see the MTA chapters of the Sun Java System Messaging Server 6.3 Administration Guide.