SendMail sending garbage mails

[Nilesh]

Hi friends,

I have some problems with my sendmail server.
it has sending some garbage mails to outside and that
mails bouncing back to on different user that is not
existing users.
the error are like 
----- The following addresses had permanent fatal
errors -----
vbqdfwhgvokn at centrum.cz
    (reason: 550 5.5.1 No such user here)

   ----- Transcript of session follows -----
... while talking to data2.centrum.cz.:

>>>>>> DATA

<<< 550 5.5.1 No such user here
550 5.1.1 vbqdfwhgvokn at centrum.cz... User unknown
<<< 503 5.5.2 Waiting for RCPT command

Subject:
Returned mail: see transcript for details
From:
Mail Delivery Subsystem <MAILER-DAEMON>
Date:
Thu, 15 Jul 2004 21:14:34 +0530
To:
vbqdfwhgvokn at centrum.cz

The original message was received at Thu, 15 Jul 2004
21:14:34 +0530
from root at localhost

   ----- The following addresses had permanent fatal
errors -----
craig at abc.net
    (reason: 550 5.1.1 User unknown)

   ----- Transcript of session follows -----
550 5.1.1 craig at abc.net... User unknown



could any one please tell me how to stop this.


		
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