dovecot-sql

driver = mysql
connect = host=127.0.0.1 dbname=mailserver user=postfix password=xxx
default_pass_scheme = MD5-CRYPT
password_query = SELECT password FROM mailbox WHERE username = '%u'
user_query = SELECT CONCAT('/home/vmail/',LCASE(`domain`),'/',LCASE(`maildir`)), 501 AS uid, 501 AS gid FROM mailbox WHERE username = '%u'