Other general architectural strategies can be undertaken to improve a site’s email performance. While these strategies stray a bit from the “making single servers perform better” guideline set down in Chapter 1, some are compelling enough to warrant mention here.
A FallbackMX host is a server set up by an organization to act as a temporary repository for queued email that is being sent from the organization to the rest of the Internet. Assuming the local domain is example.net, in M4, one can configure a FallbackMX host by adding the following line to a .mc file:
where fallback.example.net is the name of the host used as the FallbackMX host. ...