Using DNS Block Lists (DNSBLs)

Exim DNSBL Support

Exim has supported RBL from version 1.80, although the flexibility was increased (with a related change configuration options) on the release of Exim 3.00. With the release of Exim 4.00 the whole basis of policy checks on incoming mail changed to be based on a set of Access Control Lists (ACLs) applied at various during the incoming mail transaction. For this reason the configuration of Exim 4.x and later to use DNSBLs is complete different to that used for earlier versions.

Exim 4.x DNSBL Usage

In Exim 4.x a DNSBL lookup can be used in any of the incoming SMTP ACLs. However it is typical for the lookups to be used in the ACL handling RCPT TO - this allows policies to accept mail for postmaster or other special local parts (for example so a blocked sender can talk to the local postmaster about getting blocks lifted or excluded)

Exim 4.x example:

    dnslists    = : :
    message     = $sender_host_address is blacklisted in $dnslist_domain 
                  ${if def:dnslist_text { ($dnslist_text)}}



Sendmail Configuration

This page describes how configure sendmail 8.11.6 to block spam using a number of effective spam signature detection methods

First apply this patch to the source. If for some strange reason you choose not to implement any of the anti-spam rules in the .mc file this patch should be harmless.

Then ensure that your sendmail executable is compiled with MAP_REGEX defined. One way to do this is to include the line

Add these rules to the end of your .mc file, build a new .cf file with it, install, and restart sendmail to make all of the changes take effect. Don't forget to include your favorite external blacklists. Mine are:

FEATURE(`dnsbl', `', `"550 Mail from " $`'&{client_addr} " refused - see"')
FEATURE(`dnsbl', `', `"550 Mail from " $`'&{client_addr} " refused - see"')
FEATURE(`dnsbl', `', `"450 Mail from " $`'&{client_addr} " refused - see"')



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