Mail::SpamAssassin::Plugin::ASN - SpamAssassin plugin to look up the Autonomous System Number (ASN) of the connecting IP address.


 loadplugin Mail::SpamAssassin::Plugin::ASN
 asn_lookup _ASN_ _ASNCIDR_
 add_header all ASN _ASN_ _ASNCIDR_


This plugin uses DNS lookups to the services of to do the actual work. Please make sure that your use of the plugin does not overload their infrastructure - this generally means that you should not use this plugin in a high-volume environment or that you should use a local mirror of the zone (see


This plugin allows you to create template tags containing the connecting IP's AS number and route info for that AS number.

The default config will add a header that looks like this:

 X-Spam-ASN: AS24940

where "AS24940" is the ASN and "" is the route announced by that ASN where the connecting IP address came from. If the AS announces multiple networks (more/less specific), they will all be added to the _ASNCIDR_ tag, separated by spaces, eg:

 X-Spam-ASN: AS1680


The standard ruleset contains a configuration that will add a header containing ASN data to scanned messages. The bayes tokenizer will use the added header for bayes calculations, and thus affect which BAYES_* rule will trigger for a particular message.

Note that in most cases you should not score on the ASN data directly. Bayes learning will probably trigger on the _ASNCIDR_ tag, but probably not very well on the _ASN_ tag alone.

SEE ALSO - all data regarding routing, ASNs etc - SpamAssassin Issue #4770 concerning this plugin


No in-depth analysis of the usefulness of bayes tokenization of ASN data has been performed.


asn_lookup [ _ASNTAG_ _ASNCIDRTAG_ ]

Use this to lookup the ASN info in the specified zone for the first external IP address and add the AS number to the first specified tag and routing info to the second specified tag.

If no tags are specified the AS number will be added to the _ASN_ tag and the routing info will be added to the _ASNCIDR_ tag. You must specify either none or both of the tags. Tags must start and end with an underscore.

If two or more asn_lookups use the same set of template tags, the results of their lookups will be appended to each other in the template tag values in no particular order. Duplicate results will be omitted when combining results. In a similar fashion, you can also use the same template tag for both the AS number tag and the routing info tag.


  asn_lookup _ASN_ _ASNCIDR_
  asn_lookup _MYASN_ _MYASNCIDR_
  asn_lookup _ASNDATA_ _ASNDATA_