postfix mysql black/whitelist

/etc/postfix/main.cf:
smtpd_helo_restrictions = mysql:/etc/postfix/mysql_blacklist.cf

/etc/postfix/mysql_blacklist.cf:
hosts = 127.0.0.1
user = user
password = password
dbname = dbname
table = bl_mail
select_field = bl_type
where_field = address