使用C＃拒绝访问我们组织的Microsoft交流

Question

我试图从我们组织的Microsoft Exchange发送邮件，但收到错误消息：不允许客户向该服务器提交邮件。服务器的响应是：4.7.1：中继访问被拒绝

我的代码是：

private void button2_Click(object sender, EventArgs e)
    {
        string Username = "MyUsername";
        string Password = "MyPassword ";
        string SmtpServer = "OurSmtpServer";
        string From = Username + "SmtpServer ";

        System.Net.Mail.SmtpClient smtpClient = new System.Net.Mail.SmtpClient();
        NetworkCredential basicCredential = new NetworkCredential(Username, Password, SmtpServer);
        MailMessage message = new MailMessage();
        System.Net.Mail.MailAddress fromAddress = new System.Net.Mail.MailAddress(From);

        // setup up the host, increase the timeout to 5 minutes
        smtpClient.Host = SmtpServer;
        smtpClient.Port = 25;
        smtpClient.UseDefaultCredentials = false;
        //smtpClient.Credentials = basicCredential;
        smtpClient.UseDefaultCredentials = true;
        smtpClient.Timeout = (60 * 5 * 1000);

        message.From = fromAddress;
        message.Subject = " - " + DateTime.Now.Date.ToString().Split(' ')[0];
        message.IsBodyHtml = true;
        message.Body = " -88888888888888888888888888888 ";
        message.To.Add("recipient@gmail.com");



        smtpClient.Send(message);
    }

我们通常在组织中使用Windows身份验证。这是问题的原因吗？如果可以，如何在我的代码中使用Windows身份验证？

在此先感谢您的帮助！