We have a handful of Windows Mobile devices connecting to an Exchange 2007 server via ActiveSync. I have one of these devices, a Treo 700, and it has been working fine. A coworker was setup on a Cingular Treo 750 and his initially worked fine but all of a sudden after a few days now every time he sends an email from his windows mobile device via Outlook Mobile the receiver gets 2 copies of the original message back to back. I soft reset the device, checked there was nothing in the outbox, everything seems clear... The only way he is 'synching' is wirelessly with activesync.
I've seen people claim to have the same problem using other types of accounts besides exchange/outlook and they claim that hard-resetting it would work for a while but the problem just comes back after a while. I haven't gone the hard reset route because I don't want to waste my or his time, I'd rather know *why* it might be happening and start from there.