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Revision as of 13:12, 26 May 2008

DNS Lookup to Separate the domain part of a hostname

This DNS lookup helps you find the main domain part (Registrar Barrier) of a hostname. Sometimes it is reffered to as two level TLDs and three level TLDs. Lookups are accomplished through DNS calls as follows:

dig perkel.com.rb.junkemailfilter.com         - returns 127.0.0.1
dig perkel.co.uk.rb.junkemailfilter.com       - returns 127.0.0.2
dig perkel.state.ca.us.rb.junkemailfilter.com - returns 127.0.0.3

This is a service of Junk Email Filter dot com. One of many technologies used in advanced email filtering.

Exim Configuration

If you are running Exim you can use this as follows:

# This example calls rb_resolve as an ACL subroutine setting acl_c_sender_host_domain
# from $acl_c_rb_result. Using the acl subroutine allows you to extract the 
# registrar barrier part from and host string such as HELO.

warn	set acl_c_rb_query = $sender_host_name
	acl = rb_resolve
	set acl_c_sender_host_domain = $acl_c_rb_result

rb_resolve:

# Separates the domain part of a hostname - ftp.perkel.com returns perkel.com 
# DNS lookup returns 127.0.0.1 for single level domains
# DNS lookup returns 127.0.0.2 for two level domains
# DNS lookup returns 127.0.0.3 for three level domains

warn	set acl_c_rb_result =
	set acl_c_rb_query = ${lc:$acl_c_rb_query}

accept	condition = ${if eq{$acl_c_rb_query}{}}

accept	!dnslists = rb.junkemailfilter.com/$acl_c_rb_query

warn	condition = ${if eq{$dnslist_value}{127.0.0.1}}
	set acl_c_rb_result = ${sg{$acl_c_rb_query}{\N^(.*\.)?(.*\..*)$\N}{\$2}}

warn	condition = ${if eq{$dnslist_value}{127.0.0.2}}
	set acl_c_rb_result = ${sg{$acl_c_rb_query}{\N^(.*\.)?(.*\..*\..*)$\N}{\$2}}

warn	condition = ${if eq{$dnslist_value}{127.0.0.3}}
	set acl_c_rb_result = ${sg{$acl_c_rb_query}{\N^(.*\.)?(.*\..*\..*\..*)$\N}{\$2}}

accept