Google added Undo button to Gmail

Google have added an optional “undo send” feature to GMail, which allows you to quickly stop an email from going to the wrong recipient, with missing details or absent attachments. It’s part of Google Labs, which has recently added YouTube, Flickr and Picasa previews and other email tweaks.
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The feature allows five seconds for the GMail user to click “Undo” next to the standard “Your message has been sent” dialog; this returns the email to draft-status, and allows not only the recipients but text, attachments and formating to be tweaked. What it won’t do is claw back a mail that has already been sent. To use GMail Undo, go to Settings and then the Labs tab, and the option is down near the bottom of the list. We’d quite like to see a user-selectable longer time delay option in the future, but for those “oh no, I didn’t just…” moments it could be a life-saver.

Source: Slashgear.
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Suppose its a good thing if you've forgot to put summit into the e-mail or sent it to the wrong person etc.

Really wow!

they should just have an OutBox feature that you can turn off and on and every mail you send will wait in the outbox till you go into the outbox and press send or wait in the outbox for a min before sending. That way if you figure you made a mistake you can go into the outbox and just edit/delete the mail.

Yeh but most ppl wouldnt use it, ppl just want to send their e-mails straight away.
I know i just click send and then think.. hmm!! did i put everything into that, and its not the first time ive sent music to the wrong person.. but most guys just say.. hey!! cheers for the mix.