Date:  Mon, 20 Mar 2006 14:23:18 -0800
From:  "Ken Marcus -  Precision Web Hosting, Inc." <kenmarcus (at mark) precisionweb.net>
Subject:  [coba-e:04319] Re: The following recipient(s) could not be reached:   apaceh@
To:  <coba-e (at mark) bluequartz.org>
Message-Id:  <016301c64c6d$05197ae0$6700a8c0@youro1n9oy17sk>
References:  <D6B11AFC0E79FB44AA45F52E4B230EE507E107 (at mark) cow.got-milk.co.uk> <010d01c64c64$d56feac0$6700a8c0 (at mark) youro1n9oy17sk>
X-Mail-Count: 04319

>>I got that message in my inbox coming from my server:
>> Your message did not reach some or all of the intended recipients.
>>      Subject: Returned mail: see transcript for details
>>      Sent: 20/03/2006 20:13
>> 
>> The following recipient(s) could not be reached:
>>      apache (at mark) ns.nywtc.co.uk on 20/03/2006 20:13
>>            The message cannot be delivered due to a configuration error
>> on the server. Please contact your Administrator.
>>            < ns.nywtc.co.uk #5.3.0 SMTP; 553 5.3.0
>> <apache (at mark) ns.nywtc.co.uk>... No such user here>
>> 


Try adding something like this to the /etc/mail/virtusertable 
apache (at mark) ns.nywtc.co.uk        admin

# Then
makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable 

#  Then restart sendmail

/etc/rc.d/init.d/sendmail stop
sleep 5
killall -9 sendmail
/etc/rc.d/init.d/sendmail start