User welcome email

Hi, I want to send welcome email on user creation by script … welcome email is already sending when i create user but i want to check if email already exits send welcome email else dont send email…
can anyone please help me how to do that ??
any help will be highly appreciateable

you can check your condition in this file.

I am already creating a user by script, and if user exits send welcome email to that email address otherwise i dont want to send email… there is no need for password or anything else