Building Backend by using ASP.NET Web API

Here is my testing problem.

using (MailMessage mail = new MailMessage("sendermail", "recievermail"))

{

[login to view URL] = "Sending Email Using Asp.Net & C#";

[login to view URL] = "<h1>In this article you will learn how to send a email using Asp.Net & C#</h1>";

[login to view URL] = true;

SmtpClient smtp = new SmtpClient();

[login to view URL] = "[login to view URL]";

[login to view URL] = 587;

[login to view URL] = false;

[login to view URL] = true;

NetworkCredential NetworkCred = new NetworkCredential("sendermail", "XXXXXXXXX");

[login to view URL] = NetworkCred;

[login to view URL](mail);

}

Please write your bid with answer of this question.

What is this code?

Why is this error happened?

ERROR: "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at"

I will give my whole project to right candidate.