If you don't have 30 seconds to watch the above video, here's how to do it:
1. Launch Gmail.
2. Click the gear icon in the upper-right corner, then Settings.
3. Click the Labs tab.
4. Find Undo Send and click Enable.
5. Scroll down and click Save Changes.
The next time you send an email, you'll have 10 seconds to undo it. That's all she wrote.
Other tech tricks: