Table of Contents
Checking sender MX
Introduction
This check consists in checking MXs (name and address) of the domain part of the sender address against a blacklist. Some spammers use domain names with MXs defined on private networks or at IP addresses without any real machine configured at that address.
Usually you can reject messages if the domain part of the sender address can't receive mail (you can't answer him).
This kind of check doesn't block too much spam, but can alleviate mail queue from bounces to unreacheable addresses.
To enable this feature, change this option at j-chkmail.cf configuration file and define unwanted MXs at j-policy database, using BadMX prefix.
Configuration
BadMX check is enabled at j-chkmail.cf configuration file :
j-chkmail.cf
CHECK_BAD_SENDER_MX YES
The list of unwanted MXs are defined at j-policy database :
j-policy.???.txt
# # Private networks - RFC 1918 and RFC 3330 # BadMX:10 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:127 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:169.254 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:192.168 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:192.168.128.200 OK ... # # Reserved IANA - http://www.iana.org/assignments/ipv4-address-space # BadMX:0 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:1 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:2 ERROR:421:4.5.1:DNS problems... Try later ! BadMX:5 ERROR:421:4.5.1:DNS problems... Try later ! ... # Bogus MX BadMX:dev.null ERROR:421:4.5.1:DNS problems... Try later ! ... # Known spammers BadMX:saveinternet.net ERROR:421:4.5.1:DNS problems... Try later ! ... # Unprobable sender domains BadMX:client.mchsi.com ERROR:421:4.5.1:DNS problems... Try later ! BadMX:client.mchsi.net ERROR:421:4.5.1:DNS problems... Try later ! BadMX:client2.attbi.com ERROR:421:4.5.1:DNS problems... Try later ! ...
You'll find a starting list of entries at distribution file etc/j-policy.badmx.txt. This file contains entries for private networks, unassigned network addresses and a list of addresses or domains or hostnames used as MX for spam domains. List of unassigned or reserved networks or addresses you should never see comes from IANA and RFC 3330. The IANA list is updated from time to time.
