Hitting send is the best way to suddenly remember the thing you forgot to say in an email. It's also the best moment for noticing typos or suddenly realize that you shouldn't ask your ex to get back together. But what are you gonna do at that point?
Google's user experience team had the genius idea in 2009 to create an “Undo Send” feature that would hold your emails in limbo for about five seconds before actually sending them out. That way, when “Wait, I spelled her name wrong” moments came up, users could hit undo and go back to editing the email. Google put the feature in its Gmail Labs section to test it out, and users could opt in.
It just makes good sense, and now after six years, “Undo Send” has made it out of Gmail Labs and is officially part of Gmail.
Michael Leggett, who was then a Google user experience designer and now works for Facebook, wrote in March 2009, "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?"
It's an extremely useful feature, and an inconspicuous one. “Undo Send” is never in the way—it's just there if you need it. It probably didn't need to sit in Gmail Labs for so long, but now it's finally a standard option in the “General” tab of Gmail settings, and users can decide how many seconds they want Gmail to hold their emails for (5, 10, 20, or 30), before sending them out into the world.
Gmail itself had a famous five-year beta period, even as it grew massively popular. Maybe “Undo Send” was just trying to set a new record.