How to disable a mail to a user before scanning

[Harish Amin]

I receive about 50 messages to a unknown user on my SMTP server
and I as a postmaster receive all the messages back
I tried the rules

# more spam.actions.rules
To:     webmaster at www.dpi.state.wi.us    delete


# more spam.blacklist.rules
#To:     /^$/    yes
To:     webmaster at www.dpi.state.wi.us   yes

But I still keep getting it



The original message was received at Tue, 8 Jul 2003 12:08:05 -0500 (CDT)
from doagw01.doa.state.wi.us [165.189.88.161]

   ----- The following addresses had permanent fatal errors -----
<'webmaster at www.dpi.state.wi.us>
    (reason: 553 5.3.5 system config error)

   ----- Transcript of session follows -----
553 5.3.5 www.dpi.state.wi.us. config error: mail loops back to me (MX
problem?)
554 5.3.5 Local configuration error

AM I doing something wrong here...
I am running MailScanner E-Mail Virus Scanner version 4.22-4 on SUn Solaris
running sendmail
Any Help will be appreciated