# Check host's MX domain
# Looks for mx for host a.b.c.d.e
# First check d.e, then c.d.e and then b.c.d.e
deny message = No MX for host $sender_host_name domain
    hosts = ! : !+relay_from_hosts
    # Put lookup result in variable
    set acl_m8 = ${lookup dnsdb {mxh=\
    ${extract{-2}{.}{$sender_host_name}}.${extract{-1}{.}{$sender_host_name}} : \
    ${extract{-3}{.}{$sender_host_name}}.${extract{-2}{.}{$sender_host_name}}.\
    ${extract{-1}{.}{$sender_host_name}} : \
    ${extract{-4}{.}{$sender_host_name}}.${extract{-3}{.}{$sender_host_name}}.\
    ${extract{-2}{.}{$sender_host_name}}.${extract{-1}{.}{$sender_host_name}}\
    }{$value}fail}
    # Test content of variable; The MX has to be a hostname.
    condition = ${if !match {$acl_m8}{\N.*[A-Za-z].*\..*[A-Za-z].*\N}{yes}{no}}

Diemžēl katrs otrais sūtītājs sūta no adreses, kurai ir nepareizs vai neeksistējošs MX ieraksts. DNS admini - līkroči.