title: Expected response code 220 but got an empty response in laravel 5.6
body: <p>I am using mailgun with laravel 5.6 to send email but its return error( Expected response code 220 but got an empty response). The following is my all file settings.</p>
  <p><strong>.env FILE</strong></p>
  <pre><code>MAIL_DRIVER=mailgun
  MAIL_HOST=smtp.mailgun.org
  MAIL_PORT=587
  MAIL_USERNAME = postmaster@domainname 
  MAIL_PASSWORD = password
  MAILGUN_DOMAIN = domainname 
  MAILGUN_SECRET = key
  MAIL_ENCRYPTION=tls
  </code></pre>
  <p><strong>mail.php File</strong></p>
  <pre><code>&lt;?php
  
  return [
  
       'mailgun' =&gt; [
          'domain' =&gt; env('MAILGUN_DOMAIN'),
          'secret' =&gt; env('MAILGUN_SECRET'),
      ],
      'ses' =&gt; [
          'key' =&gt; env('SES_KEY'),
          'secret' =&gt; env('SES_SECRET'),
          'region' =&gt; 'us-east-1',
      ],
      'sparkpost' =&gt; [
          'secret' =&gt; env('SPARKPOST_SECRET'),
      ],
      'stripe' =&gt; [
          'model' =&gt; App\User::class,
          'key' =&gt; env('STRIPE_KEY'),
          'secret' =&gt; env('STRIPE_SECRET'),
      ],
  ];
  </code></pre>
  <p><strong>services.php File</strong></p>
  <pre><code>&lt;?php
  
  return [
      'driver' =&gt; env('MAIL_DRIVER', 'mailgun'),
      'host' =&gt; env('MAIL_HOST', 'smtp.mailgun.org'),
      'port' =&gt; env('MAIL_PORT', 587),
      'from' =&gt; ['address' =&gt; 'aakanskhi.cuminte@gmail.com', 'name' =&gt; 'Aakankshi Gupta'],
      'encryption' =&gt; env('MAIL_ENCRYPTION', 'tls'),
      'username' =&gt; env('postmaster@domain'),
      'password' =&gt; env('mailgun password'),
      'sendmail' =&gt; '/usr/sbin/sendmail -bs',
      'markdown' =&gt; [
          'theme' =&gt; 'default',
          'paths' =&gt; [
              resource_path('views/vendor/mail'),
          ],
      ],
  ];
  </code></pre>
  <pre><code>    public function testmail(){
         $user = User::findOrFail(8);
         Mail::send('emails.test',  ['user' =&gt; $user], function ($message) {
         $message-&gt;from('us@example.com', 'Laravel');
         $message-&gt;to('aakankshi.cuminte@gmail.com')-&gt;subject('Your Reminder!');
       });
      }
  </code></pre>
  <p>When I run the code it gives me following error message:</p>
  <p><strong>Swift_TransportException</strong>
  <strong>Expected response code 220 but got an empty response</strong></p>
  <p>How do I resolve this error message?</p>