Requiring password submission on the part of users logging into Messaging Server to send or receive mail is a first line of defense against unauthorized access. Messaging Server supports password-based login for its IMAP, POP, HTTP, and SMTP services.
By default, internal users must submit a password to retrieve their messages from Messaging Server. You enable or disable password login separately for POP, IMAP, and HTTP services. For more information about password login for POP IMAP, and HTTP Services, see 5.2.2 Password-Based Login.
User passwords can be transmitted from the user’s client software to your server as cleartext or in encrypted form. If both the client and your server are configured to enable SSL and both support encryption of the required strength (as explained in 23.5.2 To Enable SSL and Selecting Ciphers), encryption occurs.
User IDs and passwords are stored in your installation’s LDAP user directory. Password security criteria, such as minimum length, are determined by directory policy requirements; they are not part of Messaging Server administration.
Certificate-based login is an alternative to password-based login. It is discussed in this chapter along with the rest of SSL; see 23.5.3 To Set Up Certificate-Based Login
Challenge/response SASL mechanisms are another alternative to plaintext password login.
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.