Register Page – Already Exit Email – How can I give a good message to user without breaking privacy?

We have clearly mentioned that "we don't give personal data including email address to any third party" in our privacy policy.

So when a user try to create a account using already exit email address, I can't give a error like "Email is already registered" because it is clearly break own our privacy policy.

So what can be the process / good message to handle this situation?