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).