To block a domain from being able to send or receive mail, use the following steps.
Log into SSH and run the following commands:
touch /etc/blockeddomains echo "example.com" >> /etc/blockeddomains
Log into WHM, then go to Service Configuration > Exim Configuration Editor > Advanced Editor. In the topmostbox add the following:
domainlist blocked_domains = lsearch;/etc/blockeddomains
In the ROUTER CONFIGURATION section after the following lines:
democheck:
driver = redirect
require_files = "+/etc/demouids"
condition = "${if eq {${lookup {$originator_uid} lsearch {/etc/demouids} {$value}}}{}{false}{true}}"
allow_fail
data = :fail: demo accounts are not permitted to relay email
Add the following lines:
reject_domains: driver = redirect # RBL Blacklist incoming hosts domains = blocked_domains allow_fail data = :fail: Connection rejected: SPAM source $domain is manually blocked.
Once you have added the lines, hit Save at the bottom.