/etc/postfix/main.cf

The Postfix configuration has 300+ parameters. You are responsible to configure Postfix specifically for your needs. Here are some sample parameters. The references to the mysql*.cf are mandatory configuration options.

mydestination = <insert hostname>, localhost.$mydomain, \
    mysql:/etc/postfix/mysql-mydestination.cf
mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp 
virtual_alias_maps = hash:/etc/postfix/virtual, \
    mysql:/etc/postfix/mysql-forward.cf, \         
    mysql:/etc/postfix/mysql-virtual.cf
sender_canonical_maps = mysql:/etc/postfix/mysql-canonical.cf
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions=
 permit_mynetworks,
 permit_sasl_authenticated,
 reject_invalid_hostname,
 reject_non_fqdn_hostname, 
 reject_non_fqdn_sender,
 reject_non_fqdn_recipient,
 reject_unknown_sender_domain,
 reject_unknown_recipient_domain,
 permit_auth_destination,
 reject
smtpd_sasl_local_domain = <hostname>
smtpd_banner = $myhostname NO UCE
smtpd_helo_required = yes
disable_verify_command = yes
smtpd_client_restrictions =
 permit_mynetworks,
 permit_sasl_authenticated,
# Uncomment this if you wish to use SQLWhite,
# which is highly encouraged ;-)
# check_policy_service inet:127.0.0.1:2502,
 reject_rbl_client dnsbl.sorbs.net,
 permit

smtpd_data_restrictions=
 reject_unauth_pipelining,
 permit

(merely examples, you can choose any DNS blacklists as well as policy servers)