The second record field (for the same MX record) is the priority field. For this field, type a number that is higher than ...

The second record field (for the same MX record) is the priority field. For this field, type a number that is higher than the number for other MX records you already have. This will create an MX record that has lower priority than your other MX records.

For example, if the highest priority you have for an MX record now is set to 100, you could set the new MX record to 200.