I hope i am posting this question in the correct section and if it has been answered in the past please feel free to give me the link as i did a search in the forum and did not find a topic based on my question.
So here goes, we have a few servers VPS & dedicated servers and they are all running CentOS 7 with WHM / CPanel. What i am looking for is a way that one can blacklist/block a specific domain (not one of our domains on our servers) from sending us mail. I am aware that one could do this in cPanel / Spam Assassin, although this just allows up to five fields for complete domains you want to block. This would be a rather tedious task to perform on every cPanel account on the server, not to mention that the amount of domains we want to block is more than five so makes it pointless.
I have been reading up on some forums that there is a way to do it in the "EXIM" settings of WHM then creating a text file which you can list all the blacklisted domains in but have not managed to find clear instructions on how it is done/implemented. Any advice would be greatly appreciated while i search for all possible solutions.
PS! blocking the IP address of the sender is pointless as they sending the same spam mail 5-6 times per day and keep switching IP addresses (the only thing in the mail headers that remain constant is the domain that is sending the mail)
Thanks in advance,