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[Kaya.gs]

I have to break it to you, but all websites that use email addresses for a username, have to tell you if the address has been used before. this doesn't strike me as that scary.

I think the worry here is that it allows email addresses to be associated with particular accounts on multiple websites.

It's presumably also different to the general case if the hashed url structure (as I understand it, I haven't really been following in detail) allows rapid checking of significant numbers of addresses. Normally, unless there is an account creation API, checking for existing email addresses is much more laborious.

Thats the feature, not the worry. Right now, for example, im making a tournament organizer for OpenKaya. So people could use that site separately and by using the same email, tournament fixtures can show a user profile picture, making it easier to recognize a player you know on a server, or style it.