Ever hit send and realize immediately that you’ve made a mistake? I have! That is why I was excited when my brother told me about Gmail’s new Undo Send feature — you’ve got five seconds to reclaim that email and fix your mistake. Really!
You have to enable the tool in your Gmail account. Go to Settings (upper-right), click the Labs tab and scroll down to Undo Send. Click the Enable button and then save your changes.
And if you don’t have a Gmail account, you need to get one! The amazing search function alone makes it worth the switch.