If you use Gmail, you have probably had one or another moment where you wish you could take back the "send" click. Gmail now has an undo. Click on the tiny green beaker icon on the top of your Gmail page to open the Google Labs department for Gmail. Scroll down, or search for "undo send," and enable it.

Reload Gmail, and now, when you click send, you will gain a 5 second window to click "cancel" at the top of your screen. That will often be enough to catch those unavoidable "oops" moments. Try it on a test message to yourself. It works.  

Do you ever wonder whether that email you sent actually went out?  An easy way to keep track if you are using Outlook: Drag your Outbox up to the top left part of the screen, under the Favorite Folders heading.  Then you can see whether things are sitting around in the outbox and figure out why if they are.