在C＃中发送电子邮件而不进行身份验证

Question

我已尝试使用此代码发送电子邮件而不输入凭据：

try
{
    MailMessage mail = new MailMessage();
    SmtpClient SmtpServer = new SmtpClient("smtp server");

    mail.From = new MailAddress("sender email");
    mail.To.Add("receiver email");
    mail.Subject = "Test Mail";
    mail.Body = "This is for testing SMTP mail from GMAIL";

    SmtpServer.Port = 587;

    SmtpServer.Credentials = CredentialCache.DefaultNetworkCredentials;
    SmtpServer.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
    SmtpServer.EnableSsl = true;

    SmtpServer.Send(mail);
    MessageBox.Show("mail Send");
}
catch (Exception ex)
{
    MessageBox.Show(ex.ToString());
}

我收到此服务器错误：

  

Sytem.Net.Mail.SmtpException 5.7.3请求的操作已中止;用户未中止   authentificated

我也尝试过：

SmtpServer.UseDefaultCredentials = false;

仍然会抛出相同的异常。