Hi, I'm having repeated problems also with emails (that I have moved to folders) disappearing before my eyes when I open those folders. This started in Sept or Oct 2011 time frame, possibly after the 5.0 update?
The problem seemed to sort itself out after a month or so (while I was traveling overseas), but has recently started recurring.
I use Yahoo email. I don't have any settings in Yahoo to filter or delete automatically. In some cases if I log into Yahoo on my PC immediately after, then the missing emails appear on the PC.... and if I shut down the iPad and restart it, those will then appear on the iPad. But in some cases they are just gone forever.
I normally don't use the PC for email, so it's not a matter of my having deleted something from the server and not seeing it on the iPad later.
Regarding POP vs IMAP, that's a little over my head technically. (If you can tell me how to check, I'm certainly willing to do that.) But the Yahoo account is pretty ancient (circa 1999) so is probably set up as POP unless Yahoo has forced a change of which I'm unaware. For the iPad, I haven't a clue -- but I bought it in Feb 2011 and would have accepted the defaults/suggested settings. But until the Sep or Oct time frame it performed flawlessly so not sure what has changed.
As an aside -- mentioning only in case there's some link -- my Safari keeps crashing, often multiple times per day. This started in the past month, I think, and is becoming more frequent.
I have done full shut downs and just this morning did a reset of the iPad.
From the threads I've found here it seems to be happening to many types of email accounts, not just Yahoo.
Any thoughts or recommendations? I really appreciate this forum (head and shoulders above the apple site -- stating the obvious I guess), and hope one of you gurus can help me.
Cheers!