yum install cyrus-sasl-plain
SMTP Auth:
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain = $myhostname
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions =
permit_sasl_authenticated,
permit_mynetworks,
reject_unauth_destination