I am using the api (http) facebook some time now, but I detected a problem a few days ago ... There is people to withdraw permission email which then cause inconsistencies in the system.
There is no possibility to stop the login process if you have no access to email?
I was trying another solution. In the callback see if you have the email or not variable. The problem is that the user can not log in again because the facebook is already saved your preference not to allow email.