ipad2 email attachment comes up but then can not go back to email

You should be able to tap on the attachment and a Done button should then appear at the rop left. If it doesn't then try closing the Mail app completely and see if you can view your email when you re-open the app : from the home screen (i.e. not with the Mail app 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of the Mail app to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.

Welcome to Apple Support Communities.

In iOS 4.3.4 (the one I'm using), if the mail attachment is opens the Safari browser or some other app for viewing, you will not automatically return to Mail when you close the attachment. Click the Home button once, and then touch the Mail app icon at the bottom to return to mail. This might be "fixed" in iOS 5.0/5.1/5.1.1, but I don't know because I haven't updated yet.