A couple of things we’ve had to do in the past with regards to mail on a cPanel server have come in very handy.

Block An Email Address Sending to Server, Server Wide.

There is the option within the cPanel interface to block an email address from sending to a specific address, but if you would like to block this from sending to anyone on the server you can do this with the below instructions:

Edit the file: /etc/cpanel_exim_system_filter, and add the following lines, with the email address being placed where “” is.

if $header_from: contains “”
then
fail text “This message has been rejected”
seen finish
endif

Check Where Mail Is Being Delivered For A Domain, Local or Remote Server

This will show whether mail will be sent externally (transport = remote_smtp) and locally (router = virtual_sa_user)

exim -bt