It could be one of many issues. When we use the @unknown address, it means that we can't get the user's email address. I'm assuming your using the "Facebook User Only" option, so that the user is created automatically. If so, and the first_name.userid is coming through properly, it means that communication with Facebook is fine. We're properly getting information from the user's basic profile (their first name and userid). However, we're not getting their email address, likely because that permission wasn't granted.
In that case, check:
1) That anywhere you're allowing users to login, the button is from JFBConnect. This should prompt for the email permission properly.
2) Facebook is updating their Authorization dialog box. With this new design, users can selectively disable permissions, and you can't do anything about this. For now though, you can revert to the 'old' dialog box. In the Advanced configuration area of your Facebook app, set the "Enhanced Auth Dialog:" to disabled.
We'll be adding more features in 4.1 to improve the case where a user denies email permission.. either by redirecting to the "Full Joomla User" registration page (to get their email) or by allowing the admin to not allow users to register if they haven't given that permission. We're still investigating how we'll handle it, but for now, check the above 2 settings.
Alex
Sporadic @unknown email addresses appearing
