This is happening on both my 4S and iPad 3. The mail app will crash and/or lock and will not push any new emails. Or it will not display the email accounts at all. The only solution I have is to kill it from the springboard and re-launch it. Both are running 5.1 (4S is at build 9b179 and the iPad 3 is at build 9b176). Anyone else seeing this?