title: Symfony3.4: Exception occurred while flushing email queue: Expected response code 220 but got an empty response
body: <p>Project in symfony 3.4 framework, all functions are ready, but an exception to get errors in the process is not working because swiftmailer is not working</p>
  <p>&lt;parameters.yml&gt;
  mailer_transport: smtp
  mailer_host: &lt;&lt;--IP--&gt;
  mailer_user: email@exemple.com
  mailer_password: NULL
  mailer_port: 25</p>
  <hr />
  <p>Name                      | Transport  | Spool  | Delivery  | Single Address</p>
  <hr />
  <p>default (default mailer) |  smtp     |   YES  |   YES      |  email@exemple.com</p>
  <hr />
  <p>ERROR     [app] Exception occurred while flushing email queue: Expected response code 220 but got an empty response.</p>