MX or Mail Exchanger record specifies where mail for a domain name should be delivered. The record must be an assigned domain name, which in turn points to an IP address. MX record can have more than one domain name and the order is decided by the preferences. For example:

MX record for the domain MYSITES.COM points to MAIL.MYSITES.COM with preferences 10 (default value) and MAIL.MYWIDGETS.COM points to the IP address 203.199.83.202

If you decide to create an MX record for your domain name zone files, the email services provided in your the plan you purchased will no longer function. All email addressed with your domain name will be handled by the server you indicate in the MX record.