Sendmail frustration

[demon321]

Hello all,

I am trying to setup sendmail to do virtual hosting. I have sendmail.cw setup and my server can accept mail for the domains fine.

Suppose I have 2 domains
abc.com
xyz.com

My problem is if user@abc.com does not exist, but user@xyz.com does - user@xyz.com will get the user@abc.com's email delivered to their inbox.

How can it be setup so that if an email comes in addressed to user@abc.com - and no user account is associated with that email address - it is returned to sender?

Thanks