title: SMTP: Mailbox unavailable. The server response was: Error458 block
body: <p>I am building a C# .NET system and have my webmail Mail Client Manual Settings as below:</p>
  
  <pre><code>Username: noreply@domain.com
  Password: password123
  Incoming Server: mail.domain.com (IMAP Port: 993, POP3 Port: 995)
  Outgoing Server: mail.domain.com (SMTP Port: 465)
  </code></pre>
  
  <p>My system is trying to send out email using the following settings:</p>
  
  <p>Method 1: In controller method</p>
  
  <pre><code>MailDefinition md = new MailDefinition();
  md.From = "noreply@domain.com";
  md.IsBodyHtml = true;
  md.Subject = "subject";
  
  MailMessage mm = md.CreateMailMessage("user1@gmail.com", null, "Some Text", new System.Web.UI.Control());
  mm.From = new MailAddress("noreply@domain.com", "System Name");
  
  SmtpClient smtp = new SmtpClient();
  smtp.UseDefaultCredentials = false;
  smtp.Credentials = new NetworkCredential("noreply@domain.com", "password123");
  smtp.Host = "mail.domain.com";
  smtp.Port = 465; //tried for 25, 587
  smtp.EnableSsl = true;
  smtp.Timeout = 40000;
  smtp.Send(mm);
  </code></pre>
  
  <p>Method 2: In web.config</p>
  
  <pre><code>&lt;system.net&gt;
      &lt;mailSettings&gt;
        &lt;smtp deliveryMethod="Network" from="noreply@domain.com"&gt;
            &lt;network host="mail.domain.com" port="465" userName="noreply@domain.com" password="password123" defaultCredentials="false" enableSsl="true" /&gt;
        &lt;/smtp&gt;
      &lt;/mailSettings&gt;
  &lt;/system.net&gt;
  </code></pre>
  
  <p>I have both methods, also tried for different ports: 25, 26, 587 still having errors like The Operation has timed out.</p>
  
  <p>The error messages of different ports are as below:</p>
  
  <pre><code>Port 25: Mailbox unavailable. The server response was: Error458 block
  Port 26: Mailbox unavailable. The server response was: Error458 block
  Port 465: The operation has timed out
  Port 587: Mailbox unavailable. The server response was: Error458 block
  </code></pre>
  
  <p>Also I have searched for Error458, it meant for "Unable to queue messages for node", but no solution on how to resolve this error. Could anyone help?</p>