This seems to be a pretty common problem. You have that wonderful 1.1.1 or 1.1.2 ipod that you loaded mail on and upgraded to 1.1.3 but them something goes wrong and you have to restore it. When you do mail opens, shows the main background, and closes again. Why? leftover account "junk" from a previous installation. SSH to /private/var/mobile/Library and delete the Mail folder before upgrading to 1.1.2 and when you install the ipod apps fix, the mail application will load properly from the beginning. You can still solve this post update, but it saves the headache to do it first.