Oh dear. You didn't really mean to send that nasty e-mail to your boss, did you?
Until Thursday, your only recourse would have been the "rescind e-mail" in corporate versions of Microsoft Outlook. And that only works under certain conditions, and is useless if your boss has already opened the message.
Now Google's stepped up to the plate to save your bacon.
Its "Undo Send" feature, just added to Gmail, actually holds your outgoing e-mails for 5 seconds, giving you enough time to say "Ulp!" and cancel delivery.
To turn it on, sign in to your Gmail account, click "Settings," click on the "Labs" header and scroll almost all the way down the page to "Undo Send."
Then breathe a bit easier.