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How to undo a sent mail in Gmail?
asked Aug 30, 2010 by triuser (1,753 points)

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Unfortunately, once an email is sent through Gmail you cannot make it dissapear from the recipients mailbox nor retrieve it. Sorry!
answered Aug 31, 2010 by trianswer (22,754 points)
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Now you can do Undo in Gmail. Turn on Undo Send in Gmail Labs  under Settings, and you’ll see a new Undo link on every sent mail confirmation. Click “Undo,” and we’ll grab the message before it’s sent and take you right back to compose.Simple isn't it.
answered Aug 31, 2010 by trianswer (22,754 points)