Google added “Undo” option in Gmail to cancel the sent mails within 5 seconds window. This will make life easier for people with oops moment after sending an incomplete mail.
This is not an option to reclaim your older sent mails, because it only avoid to send a mail at that time. Gmail provide you extra 5 seconds to think and reclaim sent email. So if you realized that the mail sent by you was not complete, just click on the Undo button next to the Mail Sent Successfully Message.
To enable the “Undo” option in your Gmail account, go to the Settings and then Labs. Enable the Undo Send on Gmail from there.
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Now you can see that whenever you will send a mail by this Gmail account, you will have the option to undo the sent mail to reclaim sent messages within 5 seconds. I enabled the Undo Send on Gmail Account of mine and sent a mail to one of my close friend. Got the sent message with Undo option as you can see below,
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The Undo option appear only for 5 seconds, after that only “View Message” will be there. So go ahead and reclaim sent messages without wasting any time.