Nov 10, 2018

What is MX priority?

The MX numbers describe in which order the email servers are contacted when trying to deliver an email message. The server with the lowest MX number has the highest priority. Email sent to your domain will therefore be sent to the server with the lowest MX value. If the server with the highest priority (lowest MX value) becomes unavailable for any reason the next highest mail server will be used. If that one is also not available the next highest and so on. If two mail servers have the same MX priority one will be picked randomly by the sending server.

MX numbers are relative number between 0 and 65535 (the maximum possible MX value since it’s a 16-bit value).

Administrators like to use values like 10,20,30 instead of 1,2,3 because you can just insert another email server before or in between without having to change the existing values.