• Postfix
• Spammers_with_localhost_ptr_dns_records

Postfix/Spammers_with_localhost_ptr_dns_records

From http://archives.neohapsis.com/archives/postfix/2009-08/0350.html

Some spammers set their PTR records to return localhost, which can bypass some anti-spam measures. You can use PostConf:check_reverse_client_hostname_access and PostConf:check_helo_access to deal with these.

I use somthing like this:

smtpd_recipient_restrictions =
       ...
       check_reverse_client_hostname_access ${hash}/access_host
       check_helo_access ${hash}/access_host
       ...

to reject things like:

localhost
unreachable
.localhost
.arpa
.invalid
.inv
.test
.local
.lokaal
.localdomain
.lan
.private
.root
.adsl
.firewall
.speedportw700v
.belkin
.kornet
...

be them found in helo or in the PTR. I also use a pcre version to reject "." as PTR (among other things).