title: SmtpClient.Send gets stuck
body: <pre><code>string host = "gauntlet.asoshared.com", username= "a@a.test", pwd = "abc",
      from = "a@a.test", to = "b@b.test";
  int port = 465;
  
  var mm = new MailMessage(from, to);
  mm.Body = "b1";
  mm.Subject = "s1";
  mm.IsBodyHtml=false;
  using (var smtp=new SmtpClient(host, port)) {
      smtp.EnableSsl = true;
      smtp.Credentials = new NetworkCredential (username, pwd);
      smtp.Send(mm);
  }
  </code></pre>
  
  <p>This stays stuck on <code>smtp.Send</code>. After about 2 minutes, I get a timeout error. With Outlook it works perfectly (using my real credentials).
  Looking at Wireshark, I see a TCP SYN,SYN-ACK,ACK, and then nothing, when running this code. When using Outlook these are followed by a <code>TLSv1.2 Client Hello</code> etc.</p>
  
  <p>Tried adding the following lines at the beginning of the code:</p>
  
  <pre><code>ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) =&gt; true;
  System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
  ServicePointManager.Expect100Continue=false;
  </code></pre>
  
  <p>Why is C# getting stuck, and not even sending the <code>Client Hello</code>? </p>
  
  <p>It works fine when I use a different host.</p>
  
  <p><strong>EDIT:</strong> You can reproduce the issue yourself by running the code above <strong>as is</strong>. You will get a timeout error instead of a bad credentials error, and using wireshark, you can see that C# doesn't even attempt the TLS connection.</p>