The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

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C#

Hello,

I am getting the following error message:

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

I am using the following code:

public void sendmail()
    {
        MailMessage message = new MailMessage(new MailAddress(smtp_user_id), new MailAddress(txtemail.Text.ToString().Trim()));      
        message.Subject = "User Id and Password";
        message.Body = " :: Welcome \n\r " +
                       " \n\r " +
                       " NAME -" + " " + txtuser.Text.ToString() + " \n\r " +
                       " NO -" + " " + id.Text.ToString() + " \n\r " +
                       " USER ID -" + " " + txtmob.Text.ToString() + "\n\r" +
                       " PASSWORD -" + " " + pwd + "\n\r";
                        

        SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
        client.EnableSsl = true;
        client.UseDefaultCredentials = false;
        System.Net.NetworkCredential theCredential = new System.Net.NetworkCredential(smtp_user_id, smtp_user_pwd);
        client.Credentials = theCredential;
        client.Send(message);
    }