Локальний BLACKLIST по отправителю

“LIMIT 1” – обязательно.

acl_check_rcpt:
# ...
deny
    message   = SPAM blocked. Sender is in blacklist
    senders   = ${lookup mysql{SELECT '$sender_address' \
                    FROM `blacklist_sender_address` \
                    WHERE instr('$sender_address',`address`)>0 LIMIT 1} \

Таблицы

CREATE TABLE IF NOT EXISTS `blacklist_sender_address` (
  `address` varchar(255) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;