x1j7xJuzX

It's not a difficult problem to solve. Just let the sign-up succeed whether an account already exists for the email or not. Then say "You will receive an email with instructions to complete your registration".

If there was no existing account, send an email with the text: "An account was created for this email address at Example.com. If you requested this account, you may activate it by clicking here: https://..."

If there was an existing account, send: "An attempt was made to create a new account at Example.com for this email address, but you already have an account. If you have forgotten your password, visit https://..."