SMTP Client shows error "Requested action not taken" in C# app

I am trying to setup an email sending application, using a hotmail account.

The code looks like this:

MailMessage mail = new MailMessage(from, to);
        mail.Subject = "Proba email";
        mail.Attachments.Add(new Attachment("C:\\Documents and Settings\\Proba.txt"));
        SmtpClient client = new SmtpClient();
        client.UseDefaultCredentials = false;
        client.Port = 587; // 465 568
        client.Host = "smtp.live.com";
        client.EnableSsl = true;
        client.Credentials = new System.Net.NetworkCredential("[email protected]", "password");
        client.SendCompleted += new SendCompletedEventHandler(client_SendCompleted);
        client.SendAsync(mail, "token");

Using, Async I actually get no errors, I even get the feedback saying message sent (Event triggers) but the message never arrives. If I use the simple client.Send void, I get the following error:

5.3.4 Requested action not taken; To continue sending messages, please sign in to your account.

So any ideas on what the problem can be? As I was trying to hand down the SMTP settings of hotmail I got various setups saying port 25, then 587 so maybe it's something there. Any help would be greatly appreciated thanks!

Okay so it's definitely working now, I would just like to ask if I will have to do regular "I'm not a robot checks" or was that a one-time thing?

Solution

Here is my setup, BTW async will not return any errors.

<system.net>
<mailSettings>
  <!-- E-mail server settings -->
  <smtp from="[email protected]">
    <network host="smtp.example.com" port="25" userName="" password="" defaultCredentials="true" />
  </smtp>
</mailSettings>

    void SendEmail(EmailEntity email)
    {
        var mailMessage = new MailMessage { From = new MailAddress(email.From) };
        mailMessage.To.Add(new MailAddress(email.To));
        mailMessage.Subject = email.Subject;
        mailMessage.Body = email.Body;
        mailMessage.IsBodyHtml = true;

        // Send the email
        var client = new SmtpClient();
        client.Send(mailMessage);
    }