/etc/postfix/mysql-mydestination.cf

Create this file as root, and insert these lines. Brackets indicate server-specific information.

# mysql config file for local domain (like sendmail's sendmail.cw) 
# lookups on postfix
# comments are ok.

# the user name and password to log into the mysql server
hosts = <mysql ip>
user = mail
password = <the mysql user mail's password>
# the database name on the servers
dbname = mail

# the table name
table = domain
#
select_field = domain_name
where_field = domain_name