A MX record is a Mail Exchanger Record in DNS the denotes the mail server(s) responsible for accepting email for the specified domain. Each MX record is assigned a preference number. The lower the number, the higher the priority of the mail server.
Tech Strategies assigns at least two MX records to each account. A primary record (which generally has a priority of 10), and a secondary MX Record (which generally has a priority of 20). The secondary MX record is a backup and stores and forwards email in case the primary server is unavailable.