Restricted incoming users ruleset

[Industry Standard Computers]

Everyone:
I didn't know if this is a postfix or MS question or if someone has a 
ruleset fix for this I might have.

On one of my email servers I have "restricted users" who have no rights 
to INCOMING email.  So anyone sending in email to those accounts gets a 
bounce message like the following:

Transcript of session follows.

 Out: 220 mail.somewhere.com ESMTP Postfix
 In:  EHLO iscnetwork.com
 Out: 250-mail.somewhere.com
 Out: 250-PIPELINING
 Out: 250-SIZE 10240000
 Out: 250-VRFY
 Out: 250-ETRN
 Out: 250-AUTH DIGEST-MD5 PLAIN LOGIN CRAM-MD5
 Out: 250-AUTH=DIGEST-MD5 PLAIN LOGIN CRAM-MD5
 Out: 250 8BITMIME
 In:  MAIL FROM:<sales11 at iscnetwork.com> SIZE=1317
 Out: 250 Ok
 In:  RCPT TO:<joe at somewhere.com>
 Out: 451 Server configuration error
 In:  QUIT
 Out: 221 Bye

Any nice way to say "Sorry joe at somewhere.com cannot receive incoming 
email."  "Please send email to generic at somewhere.com."

Thanks,
Butch