Blocking non-work emails from form submissions for landing page


I’d like to know how we can block form submissions using gmail, outlook, or aol emails for this landing page: Spacebar Visuals

I’ve copied code from a different forum but it doesn’t seem to be working.

<script type="text/javascript">
    $(document).ready(function(e) {
        $('#submitbut').click(function() {
            var email = $('#email-august').val();
            var reg = /^([\w-\.]+@(?!!!!!!!!!!!!!![\w-]+\.)+[\w-]{2,4})?$/;
            if (reg.test(email)) {
                return 0;
            } else {
                alert('Please Enter Business Email Address');
                return false;