Typically for the MX Backup service you do NOT need to define a destination mail server or hosted smtp - and when setting up your new MX email backup service it should be left blank.

We will default to the lowest priority MX record that you have published for the domain. 

However there are times when you may want your mail delivered directly to your destination mail server smtp service and to ignore the published MX records. In these cases you would specify a destination server.

Some example cases of configuring the enterprise email services, would include:

• Not wanting or being able to change your MX record during an outage or maintenance
• Wanting to keep your destination server private and not expose your MX records publicly
• You would like to use an alternate port number for backup MX emails. 

NOTE: If you define a destination server for MX Backup this will take priority over your primary MX record for delivery.