cowtransfer_bypass_email.js

// ==UserScript==
// @name         CowTransfer Bypass Email Check
// @version      0.1
// @description  CowTransfer Bypass Email Check
// @match        https://cowtransfer.com/*
// @require      http://jpillora.com/xhook/dist/xhook.js
// ==/UserScript==

xhook.after(function(request, response) {
    if(request.url.indexOf('login_email_white_list') != -1) {
        response.text = '["gmail.com"]';
    }
});