Swipe - This works in Gmail, once opened you can swipe right or left to move forward / backward thru mail
If you setup another 'email account' I use hotmail, I have to return to list and select as they stated above. So the gmail app has this capability while the mail app doesn't. Too bad it's alot easier to swipe (though I don't always want to open a email, u know why and swipe would be more accident prone to this)