title: Symfony - "503 5.5.2 Need rcpt command" message when sending mail with Swiftmailer to external addrress
body: <p>I'm trying to send emails through swiftmailer in a Symfony 4 application. Here is my swiftmailer.yaml config file :</p>
  <pre><code>swiftmailer:
      mailers:
          mailer_smtp:
              url: '%env(MAILER_URL)%'
              spool: { type: 'memory' }
              transport: smtp
              host: xxxxxxxxxxxxxx
              port: 25
              encryption:
              username:
              password:
              auth_mode: login
      default_mailer: mailer_smtp
  </code></pre>
  <p>I can send emails to local addresses only, when I try to send an email to an external address I get this :</p>
  <p>app.ERROR: Exception occurred while flushing email queue: Expected response code 354 but got code &quot;503&quot;, with message &quot;503 5.5.2 Need rcpt command &quot;</p>
  <p>I have another PHP application (not using Symfony or swiftmailer) that send emails to any address (local or external) with a similar configuration :
  connection on port 25, no auth required. This is allowed on our exchange server, as long as the source IP is authorized.</p>
  <p>I changed my swiftmailer.yaml this way :</p>
  <pre><code>swiftmailer:
      mailers:
          mailer_smtp:
              url: '%env(MAILER_URL)%'
              spool: { type: 'memory' }
              transport: smtp
              host: xxxxxxxxxxxxx
              port: 25
              encryption:
              username:  xxxxxxxx@xxxxx.xx
              password: xxxxxxx
              auth_mode: login
      default_mailer: mailer_smtp
  </code></pre>
  <p>And then I get this error, to any address (external or local email) :</p>
  <p>app.ERROR: Exception occurred while flushing email queue: Failed to authenticate on SMTP server with username &quot;xxx&quot; using 0 possible authenticators. [] []</p>
  <p>If the fonction that sends the email, I'm using in the SetFrom property the same user I filled in swiftmail.yaml :</p>
  <pre><code> $message = (new Swift_Message($evenement-&gt;getNomEvenement()))
              -&gt;setFrom(&quot;xxxxxxxx@xxxxx.xx&quot;)
              -&gt;setTo($mail)
  </code></pre>
  <p>Do you have any idea to solve this?</p>
  <p>Thanks for your help</p>