Validate An Domain Name

I currently use the following code to make sure that users of my form have entered the 3 basic peices of information into my form.

<script type="text/javascript">
function validate(myform)
{
if (!myform.name.value || !myform.email.value || !myform.msg.value) {
alert('Please fill in all fields');
return false;
}
}
</script>

Now i want to make it so if they enter a email address from a specific domain (ie @garbage.com.au) it comes up with a message saying they cannot use that domain name....