It's part of their new messaging system. They started rolling it out to developer accounts a few month ago and for a while you could invite other people to the

It's part of their new messaging system. They started rolling it out to developer accounts a few month ago and for a while you could invite other people to the new system. It look like they may be rolling it out more widespread now. You can send and receive messages from your facebook email address but it's really not a highlighted feature (at least how it's currently rolled out). However, unless you are friends with the person sending you emails they currently seem to end up in your "other" folder rather than your inbox which IMO makes it to easy to miss important messages.