PAAT,
You almost had it. The instructions on this page are incorrect.
http://totalchoicehosting.com/help/id38.htm
You had: <form method="post" action="http://your.host.com/mail/src/redirect.php">
Change the "/mail/" to "/sqmail/".
I also think you have to use the host name, not your domain name.
It will look like this: <form method="post" action="http://server??.totalchoicehosting.com/sqmail/src/redirect.php">
Does anyone know how to get this javascript to auto append the domain to the username?