A Fake MX record is an extra MX record in the DNS for your domain that is created with the intent of confusing spambots.
The terms fake mx record and null mx record seems to be interchangeable and not used consistently.
Many spambots target the lowest priority (highest number) MX record hoping to hit a backup-mx spooling mail server that has weaker anti-spam mechanisms that the primary MX records for the domain.
For example you might have the existing MX records :
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
This is one of the several reasons why I don't like backup-mx services.
To create a Fake MX record you would add another MX record :
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
@ MX 30 fake-mx.example.com
The fake-mx.example.com could take a couple forms including :
I have also read about mail admins that create a fake mx record as the highest priority MX record. In this case they always use a null MX record that does not answer on port 25. I feel that this is too aggressive and should never be done since it's more likely to cause problems with you receiving email email. An example of this MX record configuration is :
@ MX 05 fake-mx1.example.com
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
@ MX 30 fake-mx2.example.com
My recommendation for your MX records would be either of the following :
@ MX 10 mail.example.com
or, if you must...
@ MX 10 mail.example.com
@ MX 20 fake-mx.example.com
Again, I don't believe there is ever a reasonable situation that would require creating MX records as both the highest and lowest priority MX records in your DNS.
The terms fake mx record and null mx record seems to be interchangeable and not used consistently.
Many spambots target the lowest priority (highest number) MX record hoping to hit a backup-mx spooling mail server that has weaker anti-spam mechanisms that the primary MX records for the domain.
For example you might have the existing MX records :
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
This is one of the several reasons why I don't like backup-mx services.
To create a Fake MX record you would add another MX record :
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
@ MX 30 fake-mx.example.com
The fake-mx.example.com could take a couple forms including :
- An A record pointing to an IP address that does not listen on port 25/tcp
- A mail mail server that always defers incoming email connections with a 4xx smtp code.
I have also read about mail admins that create a fake mx record as the highest priority MX record. In this case they always use a null MX record that does not answer on port 25. I feel that this is too aggressive and should never be done since it's more likely to cause problems with you receiving email email. An example of this MX record configuration is :
@ MX 05 fake-mx1.example.com
@ MX 10 mail.example.com
@ MX 20 backup-mx.example.com
@ MX 30 fake-mx2.example.com
My recommendation for your MX records would be either of the following :
@ MX 10 mail.example.com
or, if you must...
@ MX 10 mail.example.com
@ MX 20 fake-mx.example.com
Again, I don't believe there is ever a reasonable situation that would require creating MX records as both the highest and lowest priority MX records in your DNS.