5.1.1 User unknown bounces

[jschueler at motorcityinteractive.com]

My effort to install Cyrus has been largely successful.

I would expect to see a function to bounce email with a "5.1.1 User unknown" 
error.  But I haven't seen this function described or even acknowledged
within Cyrus.

As far as I understand, I need a hook for my MTA (Sendmail) to query.  Does 
one of the /usr/cyrus/bin utilities provide this function?  It seems easy 
enough to roll my own.  How do other Cyrus administrators handle this 
requirement?

Thanks,

Jim Schueler
Motor City Interactive