"Sometimes I regret sending a message the morning after. Other times I send a message and then immediately notice a mistake. I forget to attach a file or email the birthday girl that I can't make her surprise party. I can rush to close my browser or unplug the Internet — but Gmail almost always wins that race. An email to the wrong Larry pushed me over the edge. 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. And now you can do just that. 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." - lelapin from Bookmarklet