emerge cyrus-sasl

# ensure the following in /etc/conf.d/saslauthd:
SASLAUTHD_OPTS="${SASLAUTH_MECH} -a pam"

# just this line in /etc/sasl2/smtpd.conf 
pwcheck_method: saslauthd


# into /etc/postfix/main.cf:

smtpd_use_tls = yes
smtpd_tls_auth_only = yes

smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
#broken_sasl_auth_clients = yes
smtpd_sasl_local_domain =
#smtpd_recipient_restrictions = permit_sasl_authenticated, ....
	# smtpd_recipient_restrictions = ..., ..., 
	permit_sasl_authenticated,