Gmail has finally given its users the ultimate accessory: an Undo Send button.

No, really! You can now ‘take back’ any e-mail message you send from Gmail simply by clicking the new Undo Send link which will appear in the familar yellow advice bar above your message whenever a message has been sent.

The trick is, you’ll only have five seconds to hit ‘undo’ before the message is sent for real.

Michael Leggett, billed as a user Experience Designer at Google Labs, recently explained the rationale behind the new feature on the Official Gmail Blog:

I could undo just about any other action in Gmail — why couldn’t I undo send? Many people agreed, including Yuzo Fujishima, an engineer in the Tokyo office. My theory (which others shared) was that even just five seconds would be enough time to catch most of those regrettable emails.

So they went ahead and built it.

You can turn on Undo Send by activating the feature under Labs in the Gmail Settings screen.