This is the error that I get (domain names replaced with xxxxx)
This is the mail system at host xxxxxx.co.za.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
<thusoma@xxxxxx.co.bw>: user unknown. Command output: Invalid user
specified.
Reporting-MTA: dns; mx.connixinternet.co.za
X-Postfix-Queue-ID: A1265B5C017
X-Postfix-Sender: rfc822; ddmanbw@hotmail.com
Arrival-Date: Mon, 14 Apr 2008 09:25:55 +0200 (SAST)
Final-Recipient: rfc822; thusoma@xxxx.co.bw
Original-Recipient: rfc822;thusoma@xxxxx.co.bw
Action: failed
Status: 5.1.1
Diagnostic-Code: x-unix; Invalid user specified.
Just a man above