550 Administrative prohibition trying to setup rdns check

[renecd]

So I was going through spam to see how we could improve the spam filter, and I realized that Cpanel default allow mail from servers regardless of whether they have valid RDNS or not. I don't think that makes any sense, I know even Gmail doesn't allow this, so I went to find out how to configure this.

I found under Home »Service Configuration »Exim Configuration Manager, Advanced Editor, a setting "custom_begin_check_message_pre" which could be set to "require verify = reverse_host_lookup" which supposedly should check this.

Problem is, when I set this, it is no longer possible to send mail. The server immediately returns an error "550 Administrative prohibition".

The exim log file says "cpanel rejected after DATA: host lookup failed ( ::1 does not match any IP address for localhost)", but I have this line in /etc/hosts:

::1 localhost localhost.localdomain localhost6 localhost6.localdomain6

 

[cPanelLauren]

The host lookup on IPv6 is failing in this instance. We don't use this in the exim configuration for this reason, as well as general host lookup issues that can be found on many servers. What we use in place is SpamAssassin rules which perform rDNS lookups and score mail based on this.

The following threads go over this issue though:

Reverse DNS Lookup

In WHM I use a script called mail scanner, which lets me look at incoming and outgoing mail on the server. Problem I am seeing is that I get spammed and when I got to look into the message the hostname always says Reverse lookup failed and there mail still comes through. Is there a setting in...

forums.cpanel.net

rejecting mail connection with exim when no rDNS

Hi all i'm finding lots of spam getting thru on my server . even more getting stopped so i'm half way there. i also have configserver mailscanner setup .. nearly all the main spam now that gets thru has no reverse DNS by the looks of it. or at least that is what i see in mailwatch. so i'd...

forums.cpanel.net