/var/log/messages said:

May 11 11:15:52 ns1 postfix/trivial-rewrite[78126]: fatal: proxy:mysql:/usr/local/etc/postfix/mysql_virtual_alias_maps.cf(0,lock|fold_fix): table lookup problem
May 11 11:15:54 ns1 postfix/trivial-rewrite[78312]: fatal: proxy:mysql:/usr/local/etc/postfix/mysql_virtual_alias_maps.cf(0,lock|fold_fix): table lookup problem
May 11 11:17:33 ns1 postfix/smtp[78333]: fatal: mysql:/usr/local/etc/postfix/mysql_relay_domains.cf(0,lock|fold_fix): table lookup problem
May 11 11:17:33 ns1 postfix/smtp[78179]: fatal: mysql:/usr/local/etc/postfix/mysql_relay_domains.cf(0,lock|fold_fix): table lookup problem
May 11 11:17:34 ns1 postfix/error[78337]: fatal: mysql:/usr/local/etc/postfix/mysql_relay_domains.cf(0,lock|fold_fix): table lookup problem
May 11 11:17:34 ns1 postfix/error[78343]: fatal: mysql:/usr/local/etc/postfix/mysql_relay_domains.cf(0,lock|fold_fix): table lookup problem

ns1# postconf -d | grep relay_domains
fast_flush_domains = $relay_domains
parent_domain_matches_subdomains = debug_peer_list,fast_flush_domains,mynetworks,permit_mx_backup_networks,qmqpd_authorized_clients,relay_domains,smtpd_access_maps
proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks $sender_bcc_maps $recipient_bcc_maps $smtp_generic_maps $lmtp_generic_maps
relay_domains = $mydestination
relay_domains_reject_code = 554

in my main.cf
relay_domains = $mydestination, mysql:/usr/local/etc/postfix/mysql_relay_domains.cf

why ???
thanks!