Facebook is home to more than half a million apps and some of these apps would like to know your actual email address before you can add them to your Facebook profile.
For instance, if you are planning to play Farmville or CityVille or any of the other popular games on Facebook, you’ll be required to share your email address with the game developer, Zynga in this case (see the above screenshot).
If you would like to avoid sharing your email address with the developer and yet use their Facebook app, just click Change under “Send me email” and Facebook will offer you a new and anonymous email address that you can share with the app developer.
Any messages sent to this address will still reach your main inbox but your actual email address will stay hidden from the app developer. Also, once you decide to remove the game /app from your Facebook profile, that proxy email address will be gone too. Simple!
Also see: How to Block all Facebook Apps Forever!