Emails not sending from smtp.zoho.com in c#

Question

I am using ZOHO mail server for sending mails through my application. But it gives following error -

 

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

 

my code -

MailMessage msg = new MailMessage();
msg.To.Add(new MailAddress("[e-mail]"));
msg.Bcc.Add(new MailAddress("[e-mail]"));
msg.From = new MailAddress("[e-mail]", "Test mail");
msg.Subject = "send mail";
msg.Body = "test MAIL....";
msg.IsBodyHtml = true;
SmtpClient client = new SmtpClient();
client.Host = "smtp.zoho.com";
client.Credentials = new System.Net.NetworkCredential("[e-mail]", "XXX");
client.Port = 587;
client.EnableSsl = true;
client.Send(msg);

please give a solution ..