Hash a value with itself as salt

Question

I'm developing an application where users can search for other users that are already registered with their email. But because I don't want people to send me the addresses of their whole contact book in plaintext I was thinking about some SHA512 magic:

The client appends every email to itself:

hash = sha512(email + email)

And the server is doing the very same thing when registering a new user. (Once an email is registered I will store it plaintext as well as hashed for database lookups and account recovery and stuff)

Please note that this is nothing critical. I just want to make sure that you can't check those emails by simple google the hash or by mathematical calculations base on how sha512 works. Just in case my database gets leaked.

Should this do the job (or is it completly useless in comparison to a simple sha512 hash?). Or is there a better approach to get this?

Thanks in advance

Answer 1

This is useless comparing to simple hash.