Some unusual Postfix errors

I currently have several people using my web/email server for mail relaying (The server is setup as a virtual hosting box).

They all seem to be relaying fine besides one user. Below is one of the error return emails in full from this user:

-----Original Message-----
From: The Post Office [mailto:postmaster@userone.co.uk]
Sent: 04 April 2006 22:04
To: auser@userone.co.uk
Subject: Error

The original message was received at Tue, 4 Apr 2006 22:03:32 +0100 from
userone.co.uk [78.247.48.18]

----- The following addresses had permanent fatal errors -----
<auser@userone.co.uk>

----- Transcript of session follows -----
  while talking to userone.co.uk.:
>>> MAIL From:"The Post Office" <postmaster@userone.co.uk>
<<< 501 "The Post Office" <postmaster@userone.co.uk>... Refused

There was also another email error which reported that "domain1.com loops back to myself". Yet domain1.com is a domain somewhere else in the world which has nothing to do with the relay server - It was just someone the user was E-mailing.

My first thought is that there's a virus, but i'm hoping someone with a bit more Postfix knowledge might know otherwise.

Thanks.
LVL 4
wbstechAsked:
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Cyclops3590Commented:
as to the loop I'm not sure with looking at the configs and the logs
but this link shows what the 501 error is, now to track down exactly what happened you'd have to turn on verbose logging and wait until it happens again, then look thru the logs

url:  http://www.qksoft.com/qk-smtp-server/smtp-error-501.html

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wbstechAuthor Commented:
That should do the trick - I Googled that one aswell, found out about debug_peer_list and all that jazz. Thanks for the help.
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