From LedHed's Wiki
Postfix supports SASL (Simple Authentication and Security Layer)
As if version 2.3.x Postfix supports Dovecot's SASL server implementation. See Postfix & Dovecot-Auth
SMTP_SASL
smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes
smtpd_sasl_security_options = noanonymous
smtpd_recipient_restrictions =
.........
permit_sasl_authenticated
.........
.........
Also See: SMTPD Recipient Restrictions