Like all meteors, Mailmeteor can end up crashing. You may get an error message: "Oops- That's an error. An unexpected error has occured. We have been notified and are working on it."
This error may occur for different reason, and especially when you are using multiple Google accounts. This issue is known and has been reported to Google for investigation.
If you still need a helping hand on this, contact us. We'll be glad to help!