It seems that Blizzard blessed us with another change. Mail with no longer bounce back after 30 days and it will simply be lost. So if you're like me and use the mail system as another form of inventory management, you'll need to through the mail boxes on all of your alts and make sure anything you want to keep won't be lost.
The Return button also is gone, so you'll need to manually remove things from the mail and send them back to where you want them.
I'm hoping this is a change that gets reverted.... :(