root@filter-1:/etc/postfix# postconf -n
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
disable_mime_output_conversion = no
html_directory = no
mail_owner = postfix
mailq_path = /usr/bin/mailq
manpage_directory = /usr/local/man
newaliases_path = /usr/bin/newaliases
queue_directory = /var/spool/postfix
readme_directory = no
recipient_delimiter = +
sample_directory = /etc/postfix
sendmail_path = /usr/sbin/sendmail
setgid_group = postdrop
transport_maps = proxy:mysql:/etc/postfix/sql-virtual-transport.cf
unknown_client_reject_code = 550
unknown_local_recipient_reject_code = 550

root@filter-1:/etc/postfix# cat sql-virtual-transport.cf
user = dbmail
password = *******
hosts = 127.0.0.1
dbname = dbmail
query = SELECT transport
        FROM dbmail_domains
        WHERE domainName = '%s'

May  5 14:18:58 filter-1 postfix/lmtp[19473]: fatal: valid hostname or network address required in server description: 192.168.1.61:28,lmtp:192.168.1.61:28,lmtp:192.168.1.61:28
May  5 14:18:58 filter-1 postfix/lmtp[19474]: fatal: valid hostname or network address required in server description: 192.168.1.61:28,lmtp:192.168.1.61:28,lmtp:192.168.1.61:28
May  5 14:18:58 filter-1 postfix/lmtp[19475]: fatal: valid hostname or network address required in server description: 192.168.1.61:28,lmtp:192.168.1.61:28
May  5 14:18:58 filter-1 postfix/lmtp[19476]: fatal: valid hostname or network address required in server description: 192.168.1.61:28,lmtp:192.168.1.61:28
May  5 14:18:58 filter-1 postfix/lmtp[19477]: fatal: valid hostname or network address required in server description: 192.168.1.61:28,lmtp:192.168.1.61:28


mysql> select * from dbmail_domains WHERE domainName LIKE 'xxxx.co.uk';
+------+------------+-------------+----------------------+-------+---------------+
| ID   | domainName | client_idnr | transport            | plesk | dbmail_island |
+------+------------+-------------+----------------------+-------+---------------+
| 4280 | xxxx.co.uk |           0 | lmtp:192.168.1.61:28 |     1 |             1 |
+------+------------+-------------+----------------------+-------+---------------+
1 row in set (0.00 sec)