The domain's MX Records control where email that is sent to your domain will go.
This tells all email messages addressed to your domain to go to your domains 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.
It also 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.
You only need to modify your MX Records if you host a domain and host your email account somewhere else.