GPII-1707:  Moved firing of `onMessageReceived` so that it consistently fires once the message file is written. Hopefully will resolve intermittent Windows test failures.
GPII-1707:  Moved firing of `onMessageReceived` so that it consistently fires once the message file is written. Hopefully will resolve intermittent Windows test failures.

the-t-in-rtf/gpii-mail-test,GPII/gpii-mail-test