Why protonmail mail is not receving any email from other email account

Cant receive mails from other email accounts

I just got the invitation from protonmail and i registered the account there. I can send emails to other email accounts but i can't receive emails.This is the error being generated by Notify@protonmail.ch

"Hi, User @protonmail.ch doesn't exist. Please check the email address again. Thank you! ProtonMail"

But i have already registered it and its working perfectly.