What is FakeMX?
FakeMX (also known as SMTP Fake MX) is an email service that sits at the lowest priority of servers for a domain and fights against the spammers.
Many SPAM mails are sent to the lowest priority mail server in the hope that you have less anti-spam systems in place to deal with the mails, others may randomly pick an MX server to send to.
Legitimate email is normally sent to the highest priority mail server that is online, if mail to this server fails then a lower priority servers is tried.
Any email that tries the Fake MX server receives a SMTP 451 Temporary error and told to try again. At this point the majority of spam gives up and moves onto the next victim, whereas legitimate email will retry using a different mail server in the DNS MX list.