If your application expects to see incoming mail in the myApp1 folder, the messages should be sent to myApp1%File@your.communigate.domain.
In this case one can send messages to myApp1@your.communigate.domain: the myApp1 is treated as a local user name, so the Alias records will be checked first. As a result, messages will be redirected to MyApp1@File, and the CommuniGate File module will store them in the MyApp1 folder.