My experience is completely different. I am using Modest with Gmail IMAP, and it works really well. No more internal errors from I am using the pre-release diablo (and now with the official). I have an account with no many email (aprox. 5k). No crashes, it notify perfectly and so on. Rtcomm have crashed randomly, it sometimes duplicate contacts, change the fields in the contacts app, and some other thing. It isn't important to me, but in my experience Modest is more stable than Rtcomm.