cPanel, email, and the difference in fail and blackhole
If you’re running a server with cPanel and using exim as your mail server you have two semi-unlisted options for handling mail that’s not to a specific address.
cPanel calls this a catch all address and it’s useful if you want to have mails addressed to incorrect addresses on your domain still get to you. The problem that arises is that when every invalid address gets forwarded to you you will start getting all sorts of spam. One of the favorite techniques of spammers is to send out emails with random names appended to known domains. So they might send emails to bob@example.com, bob0001@example.com, bob0002@ex…., well, you get the idea. It works better for the spammer on domains like gmail.com or aol.com, but I’ve had several spammers do the same with my domains.
That led me to turn off the catch-all email because I was literally getting hundreds of spam messages a day.
Aside from just leaving the address blank, you have two options for a catch-all address. You can put either :fail: or :blackhole: (make sure you have the colons in front and behind) in as the catch-all address and exim will treat it a little differently. :fail: causes the message to bounce just like it should if the address doesn’t exist and :blackhole: just causes the message to disappear.
So which to use?
My suggestion would be to use :fail: The biggest reason is that it behaves like a server should when an address doesn’t exist - it sends back a message to the sender that the address is invalid. A major problem with :blackhole: is that the message still has to be processed and can stay in the exim queue for several days before the server finally decides to discard it. And possibly even a more significant problem is that because :blackhole: messages are still processed they take CPU and memory resources to handle. :fail: messages just bounce off with minimal processing.
ConfigServer.com has a pretty good article on why using :fail: is a good idea.
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