What Google announced today is actually more of a delay send feature, but it's the kind of thing that could save you from accidentally sending a message to your boss that was meant for your mom.
You'll have the option to delay your emails by 5, 10, 20, or 30 seconds, which might be all the time you need to catch a wrong address or misspelling.
Once you've navigated to the settings 
page, selected your time delay, and hit save, you'll see a little window pop up after each email prompting you to "Undo" or "View Message."
I would still recommend proofreading your emails before you hit the send button, but it's always nice to have a safety net for the occasional slip up!
