Temporarily reject mail directed at low-priority mail servers with FakeMX. In addition to your email spam-filter FakeMX adds to your spam level protection.
Typically most companies install email spam filters on their highest priority mail server (smallest DNS MX number) only. Meaning that some spammers will target the lowest priority mail server (largest DNS MX number). In most cases companies and ISPs (Internet Service Providers) offer two mail servers, the primary mail server with the spam filtering solution running and the secondary mail server acting as a backup.
Spammers love the lower priority (larger DNS MX number) mail servers because they are less protected and more susceptible to abuse. This is where FakeMX fits into the protection arsenal.
FakeMX sits at the lowest priority (highest DNS MX number) and is the last mail server on your list of MX servers. All mail attempts for registered domains will be temporary rejected with a SMTP 451 Error, which basically means "Try again later". A good mail server will do just that and try again later but using a different mail server in your MX list; but most spamming software simply gives up and moves on to the next target.
Please note FakeMX is another spam fighting tool against spammers, it works in conjunction with your spam filter solution to further help combat the battle of junk unsolicited emails.
In your DNS (Domain Name Service) records you will have for your domain DNS records of type MX (Mail eXchange). These records have a priority typically from 1 to 99 (but these number may be different for your domain). The smaller the number the higher the priority of the mail server.
Let's say we have three mail servers and the DNS records are:
When a downstream mail server tries to deliver email for the domain example.com it will do a look up on the MX records for the smallest MX number (meaning the highest priority of mail server, i.e. mx1.example.com) and deliver email to that server. If that server is busy or unavailable the downstream server tries the next mail server on the next larger MX number (in this case mx2.example.com)