Facebook tries to force you to use their email
Forbs recently noticed that Facebook suddenly and basically without warning made @facebook.com your default visible email address on your timeline.
I had no idea that such an email address even existed! I certainly don’t check it explicitly. Emails to that address end up in your standard Facebook messages queue, which for me is mostly a black hole.
LifeHacker has a nice article on how to change the settings back to how you might want them.
You may not want some spammer to get that address and start filling up your Facebook messages queue.