Issue Calling AJAX script from a subdomain (ExpressionEngine)

Question

I have a site with a main domain with several subdomains. I use an AJAX call to send out emails. It works fine from the main site (www), but not the microsites. My file structure is:

/www
   emailsend.php

   /sub1
       emailsend.php
   /sub2
       emailsend.php
   /sub3 
       emailsend.php

And the domains are www.hawksite.com, sub1.hawksite.com, sub2.hawksite.com, sub3.hawksite.com. Here is the call:

    $.ajax({
      url: "/emailsend.php",
      data: { loc: locString, mes: message}
    });

When I check the inspector, the xhr request is to

http://sub1.hawksite.com/emainsend.php

but I get a 404 not found error. The site is built in Expression Engine if that makes any difference.