Sending mail using external SMTP server uses IP not defined in Azure Web Apps' Outgoing IPs
<p>I have an Azure Web App. When I'm attempting to send an email using my external SMTP server, the source IP from Azure is not one of the ones listed in the Web App's "Outgoing IPs". I need to reliably know what the source IPs may be so I can whitelist it on my SMTP server. Does anyone know why this may be? </p>

<p>If it helps, here's some test code.</p>

<pre><code>    private void SendTestEmail()
    {
        SmtpClient client = new SmtpClient();
        MailMessage mail = new MailMessage();
        mail.To.Add(RECIPIENT_EMAIL);
        mail.Subject = "TEST subject";
        mail.Body = "This is a test&lt;BR&gt;&lt;BR&gt;&lt;BR&gt;";
        mail.IsBodyHtml = true;
        mail.From = new MailAddress("myemail@mydomain.com", "Testing");
        mail.Body += "&lt;div class=eventBody&gt;This is a test&lt;/div&gt;&lt;BR&gt;&lt;BR&gt;";

        client.Send(mail);
    }
</code></pre>

<p>The SMTP server address is defined in the web.config and works from known IPs:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
&lt;configuration&gt;
  &lt;system.net&gt;
    &lt;mailSettings&gt;
      &lt;smtp&gt;
        &lt;network host="mysmtpservernamegoeshere" /&gt;
      &lt;/smtp&gt;
    &lt;/mailSettings&gt;
  &lt;/system.net&gt;
&lt;/configuration&gt;
</code></pre>