How to restrict only 1 domain email during reg. & how to set new value to be unique?

[hivehost]

Thank you for your reply.

Yes, I had a look at that page already. And I found the line of the input box for Staff Id as follows.

<input type="text" class="bginput" name="userfield[field6]" id="ctb_field6" value="" size="25" maxlength="100" />

But I need the php variable name which holds the staff id which is the value stored in userfield[field6]. This variable should be able to be found at /includes/class_dm_user.php, but I am unable to find it.

Just as $email holds the email address the user entered, there must be something which holds this staff id value.

I suppose if I am able to get the php variable that holds the staff id, I should be able to compare and make sure that there is no duplication of the staff id in the db.