フリーメールドメイン一覧と法人メールチェック

<script>
/* Work email only: stops the form when the address is from a common
   free-mail service and shows a message at the field. It runs in the
   visitor's browser and can be bypassed: treat it as a hint, and check
   again where the form data arrives. */
(function () {
  var BLOCK = ['gmail.com', 'googlemail.com', 'yahoo.com', 'hotmail.com',
    'outlook.com', 'live.com', 'msn.com', 'icloud.com', 'me.com', 'aol.com',
    'proton.me', 'protonmail.com', 'gmx.de', 'gmx.net', 'gmx.at', 'gmx.ch',
    'web.de', 't-online.de', 'freenet.de', 'yahoo.de', 'hotmail.de', 'outlook.de'];
  var MESSAGE = 'Please use your work email address.';
  document.querySelectorAll('form').forEach(function (form) {
    var field = form.querySelector('input[type="email"], input[name*="email" i]');
    if (field === null) return;
    function check() {
      var domain = field.value.trim().toLowerCase().split('@').pop();
      field.setCustomValidity(BLOCK.indexOf(domain) > -1 ? MESSAGE : '');
    }
    field.addEventListener('input', check);
    form.addEventListener('submit', function (event) {
      check();
      if (field.checkValidity()) return;
      event.preventDefault();
      field.reportValidity();
    }, true);
  });
})();
</script>