fix: Update config to be flexible for host

common/models/user.js

@@ -12,6 +12,7 @@ import { blacklistedUsernames } from '../../server/utils/constants';
 const debug = debugFactory('fcc:user:remote');
 const BROWNIEPOINTS_TIMEOUT = [1, 'hour'];
 const isDev = process.env.NODE_ENV !== 'production';
+const devHost = process.env.HOST || 'localhost';
 
 function getAboutProfile({
   username,
@@ -443,7 +444,7 @@ module.exports = function(User) {
           from: 'Team@freecodecamp.com',
           subject: 'Welcome to freeCodeCamp!',
           protocol: isDev ? null : 'https',
-          host: isDev ? 'localhost' : 'freecodecamp.com',
+          host: isDev ? devHost : 'freecodecamp.com',
           port: isDev ? null : 443,
           template: path.join(
             __dirname,