What's an MX record?
Mail servers send and receive email messages on the Internet. MX (Mail Exchanger) records specify and prioritize the incoming mail servers that receive email messages sent to your domain name. There is often no need to modify your MX records. Sometimes you have to update them if you host a website with one network (such as ours) but you have email hosted in another.
Normally, you have multiple MX records assigned to your domain name, which can prevent lost email messages during an outage. Each MX record has a priority, or a number to designate the order in which your domain name's incoming mail servers receive your email messages. The MX record with the lowest number is the first, or primary, mail server to which outgoing mail servers attempt to deliver your email messages.
For example, MX0 is assigned the value 'mail.coolexample.com'. This tells all email messages addressed to your domain to go to your domain's mail server where you can pick it up. You may have multiple MX records assigned, for example MX10, MX20, and MX30 may also be assigned a mail server. This is a fail-safe measure you can use in the event your default mail server is down. The alternate mail servers store your email messages until your default server is back online. This prevents loss of email messages during your main mail server's downtime. This is called MX Priority. The lowest number MX record is the first one attempted for delivery.