cognito pre-signup

Hello

I try to put a condition to only allow email addresses from my own domain to sign up for the cognito user pool. I tried the pre-signup trigger and a lambda function to check the information passed;however I was able to automatically confirm users with email addresses from my own domain but other domain email addresses were still accepted as unconfirmed.
Is there a way to stop the processes if the email provided is from a different domain?

thanks
RT