Disable email

Hi, is there any way of disabling email for some domains? I have a problem where emails from Wordpress CF7 fail to deliver (bounced, user unknown).

Some domains do deliver some of them do not. I was looking for a correlation between e_domains DB and the message, so it appears to be that if the email is created when creating the domain then it will try to look up for such user, and if it fails to do so then it will bounce.

Is this correct? And if it is, how I can disable emails for some domains so Postfix delivers directly to the “outside”?