same happened with me yesterday: i replied to several msgs while aboard flight, using the "all inboxes" feature. i even edited one of the replies from the "outbox". while waiting in the immigration queue, i connected to the airport wifi, downloaded and replied to several additional msgs. These relating to my gmail account were sent and appear in the gmail sent folder, and these relating to my exchange account just disappeared. been using ipad in the same way for about 2 years, but just upgraded to ipad 2.