Email Hashes on Facebook

I have a question about email hash on facebook if the email address has been changed by the facebook user.

My 开发者_运维问答site stored the email hash to match with the facebook email hash to identify the user on our website is the same user on our facebook application. If a facebook user has two facebook account with different email address, and one has the email hash registered through our website. At this point, if the facebook user rearrange the email address with another account, what will happen with the email hash...

That is not exactly how you are supposed to make use of the email hash provided by Facebook Connect. The idea is that you will be able to confirm if you have the same email address for the user on record as they use on Facebook. To identify users, you should be using a mapping of your site's native user id system and the user id that Facebook provides.

I recommend that you read the documentation provided by Facebook:

http://wiki.developers.facebook.com/index.php/Connect/Authentication_and_Authorization

And this excellent tutorial by Goldstein Technologies:

http://www.goldsteintech.com/facebook_connect/tutorial.php