It is very important that Facebook Connect and Facebook app users aren’t duplicated in our website. So if they already have an account on our website, when they connect through FB Connect or our Facebook app, we want to link rather than create another account. We typically do so by matching email addresses.
So I was excited to see an FQL field for email_hashes in the user object. However, that doesn’t return anything. I think I need to use the connect.registerUsers REST api function to first send facebook all the email hashes for my users. That’s fine, but that mechanism is now deprecated.
Is there a way to get email hashes from Facebook users?
The only way still is as you detailed and as is documented on connect.registerUsers. email_hashes will be populated if you first call connect.registerUsers and there is a email match. I wouldn’t be too concerned about it being deprecated as I am guessing they won’t remove this functionality without first migrating it the the graph api as they say they will do on the documentation page.