sending mail in mvc

Question

please help me to solve

 

error->Additional information: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. 

 

my code is like below 

[HttpPost]
public ViewResult Index(mail_sending.Models.MailModel _objModelMail)
{
if (ModelState.IsValid)
{
MailMessage mail = new MailMessage();
mail.To.Add(_objModelMail.To);
mail.From = new MailAddress(_objModelMail.From);
mail.Subject = _objModelMail.Subject;
string Body = _objModelMail.Body;
mail.Body = Body;
mail.IsBodyHtml = true;
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.gmail.com";
smtp.Port = 587;
smtp.UseDefaultCredentials = false;
smtp.Credentials = new System.Net.NetworkCredential("[email protected]", "shushiladevi"); // Enter seders User name and password
smtp.EnableSsl = true;
smtp.Send(mail);
return View("Index", _objModelMail);
}
else
{
return View();
}
}