Tzakuk - 3:03 pm on Jun 6, 2012 (gmt 0) [edited by: Tzakuk at 3:21 pm (utc) on Jun 6, 2012]
If you are only dealing with a single domain, you only need to have the client enter the local-part of their email address, and you provide the '@yourdomain.edu' This way there is no option for anyone to enter another domain name and there is no need to test.
If you are dealing with several domains, you could make a drop-down available for the user to select the appropriate domain from a list.
<p>Enter your email user name</p>
<form method="post" action="yourMailScript.php">
<input type="text" name="name" size="64" />
<input type="submit" name="submit" value="send" />
This is the simplest solution I can think of. Hope it helps you.
[edited by: Tzakuk at 3:21 pm (utc) on Jun 6, 2012]