você pode integrar facilmente o postfix com o dovecot sasl e fazer a interface dovecot com o MySQL. Dê uma olhada em: link e link
Eu uso com sucesso o sigma postfix + dovecot com autenticação de arquivo de senha:
dovecot cfg:
protocols = none
listen = 127.0.0.1
first_valid_uid = 89
auth_verbose = yes
auth default {
mechanisms = plain login
passdb passwd-file {
args = /etc/postfix/smtpd.auth.passwd
}
userdb static {
args = uid=89 gid=89 home=/var/mail/null/
}
user = root
count = 5
socket listen {
client {
path = /var/spool/postfix/private/auth
mode = 0660
user = postfix
group = postfix
}
}
}
parte do postfix cfg:
smtpd_recipient_restrictions =
permit_mynetworks,
permit_sasl_authenticated,
reject
# postfix-dovecot SASL options
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_sasl_tls_security_options = $smtpd_sasl_security_options
# report sasl login name in Received: message headers
smtpd_sasl_authenticated_header = yes
# TLS/SSL configuration
smtpd_tls_cert_file = /etc/postfix/ssl/server-cert.pem
smtpd_tls_key_file = /etc/postfix/ssl/server-key.pem
###cat server_cert.pem intermediate_CA.pem > server.pem
#smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem
smtpd_tls_received_header = yes
smtpd_tls_security_level = may
smtpd_use_tls = yes