Send Email in C# using NTLM

Question

I need to send email using NTLM, currently, I'm using the following code to send email

SmtpClient objSmtpClient;
        System.Net.NetworkCredential objNetworkCredential;
        objSmtpClient = new SmtpClient("10.xxx.xxx.xxx", 587);
        objSmtpClient.EnableSsl = true;
        objNetworkCredential = new System.Net.NetworkCredential(userName, password);
        try
        {
            string to = txtto.Text;
            MailMessage objMailMessage = new MailMessage();
            objMailMessage.From = new MailAddress("from@email.com", "sendername");
            objMailMessage.To.Add(new MailAddress("to@email.com"));
            objMailMessage.Subject = "subject";
            objMailMessage.Body = "body";
            objMailMessage.IsBodyHtml = true;
            objSmtpClient.EnableSsl = true;
            objSmtpClient.UseDefaultCredentials = true;
            objSmtpClient.Credentials = objNetworkCredential;
            objSmtpClient.Send(objMailMessage);
        }
        catch (Exception ex)
        {
         MessageBox.Show(ex.Message + " INNER EXCEPTION > "+ex.InnerException +" DATA > "+ex.Data);  
        }

The Above code works if I try to change the port to 25 and EnableSSL to false, But when I try to send it using 587 and setting EnableSSL to true it doesn't work.

I'm getting the following error, sometimes I get an Invalid Certificate error.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.1 Client was not authenticated.

I am also getting this error

I think the problem is with Authentication, how can I force to use NTLM

I talked with the IT team they installed a tool on my pc to check email, using that tool email was sent successfully.

The following are the setting which he applied in that tool

Can someone please help

Answer 1

我正在测试，我遇到了同样的问题，我通过禁用 SSL 安全来修复它

SC.EnableSsl = false;