The “Reverse DNS lookup” is to check the DNS name (Hostname) from the IP address for senders mail address, if the reverse DNS is set for the senders e-mail server ip address then only e-mail will be deliver on the server else it will bounce back to the sender with no Reverse DNS for E-mail server ip address message.
We can enable the “Reverse DNS” lookup in the Exim with the following steps.
1) SSH to the server with the root login details and edit the exim.conf with your favourite editor.
pico exim.conf
Search the following line and change it
From
#host_lookup = 0.0.0.0/0
To
host_lookup = 0.0.0.0/0
It will enable the “Reverse DNS” lookup for all the incoming connections.
If you are not having the shell access then Login into WHM and select the following option and make the above changes.
WHM >> Service Configuration >> Exim Configuration Editor >> Advanced exim configuration editor
