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 is an extension to the SMTP protocol that allows clients to authenticate to the server. The authentication accompanies the message. The primary use of authenticated SMTP is to allow local users who are travelling (or using their home ISP) to submit mail (relay mail) without creating an open relay that others can abuse. The “AUTH” command is used by the client to authenticate to the server.
For instructions on enabling SMTP password login (and thus Authenticated SMTP), see 12.4.4 SMTP Authentication, SASL, and TLS.
You can use Authenticated SMTP with or without SSL encryption.