I'm doing some work on social logins (connecting with Facebook, Twitter,
Google+ and the lot) and in setting it up so that existing users would be
connected to their account rather than registered again when using the
social login feature, I realised - to my surprise - that the email field in
elgg_users_entity is not a unique key.
I'm just curious to know whether this was a conscious choice and what the
reasoning behind it was, as in pretty much all social networks I know of a
user is only allowed to register an email address once.