For anyone who's ever sent an angry/pathetic/embarrassing email that they've instantly regretted, Gmail's experimental "Undo Send" feature has been a lifesaver. Now, it's becoming an official part of Gmail on the web. The feature lets you instantly retract an email shortly after you've hit the send button. It was one of the first truly useful Gmail Labs offerings, a collection of experimental features mainly meant for power users. Mostly, we wonder what took Google so long to make it part of the core Gmail experience. Undo Send is disabled by default (which doesn't make much sense), but you'll eventually see it as an option in your "General" Gmail settings tab in the coming weeks. If you've already enabled it from Gmail Labs, however, it'll be turned on by default.