Alerts users to whilte-list your email address whenever they submit a form. Alerts could be customized to appear for only selected domain names like aol.com, earthlink.net etc.

whitelist-alert

//Script assumes that you have jQuery loaded. Most WordPress themes do.
jQuery(document).ready(function(){
  //Check email addresses
  //All domains have to be be lower case
  var check_emails = new Array("earthlink.net", "aol.com");
  var email_warning = "Please make sure to white-list our email address test@test.com so it doesn't get stuck in your SPAM folder.";
  var form_selector = 'form'; //change to '#form_id' - to apply to a specific form ID.
  jQuery(form_selector).submit(function(){        
    jQuery('input').each(function(){
      //check if form field values contain @ - we assume that's email address
      var field_value = jQuery(this).val();
      if( field_value.indexOf('@') != -1 ){
        var parts = field_value.split('@');
        //Get the domain part of the email
        var check_domain = jQuery.trim( parts.splice(1,1) ).toLowerCase();        
        //Check if emails array has values        
        if( check_emails.length > 0 ){
          //see if newly entered domain is in the predefined array          
          if( check_emails.indexOf(check_domain) != -1 ){
            alert( email_warning );
          }          
        }else{
          //If no domains defined, we assume that warning applies to all emails.
          alert( email_warning );
        }
      }
    });
  });
});