Facebook has abruptly switched everyone's default email address to the @facebook.com account you've never used. So how do you switch it back? Because you'll want people to contact you.
A while back ago, Facebook launched a Facebook email system that, sadly, no one used. But if you go to your profile today, you'll see the @facebook.com email account listed, which forwards to your Facebook messages inbox and none of your others. It's a hidden attempt to make the Facebook inbox relevant, or replace email as they probably want it.
There's a way to reverse this. Go to your Timeline, click about, under your contacts info. Then scroll down to "Contact Info" and hit edit and switch all of the crossed out circle symbols to a full circle for each inbox you want visible on your profile.
If you don't want @facebook.com to show up switch it from a full circle to crossed out (which means Hidden From Timeline). Then hit save.
Update: A Facebook spokesperson provided the following non-explanation to Reuters:
As we announced back in April, we've been updating addresses on Facebook to make them consistent across our site.
In addition to everyone receiving an address, we're also rolling out a new setting that gives people the choice to decide which addresses they want to show on their timelines.
Ever since the launch of timeline, people have had the ability to control what posts they want to show or hide on their own timelines, and today we're extending that to other information they post, starting with the Facebook address.