Web Forms :: MTP Server Requires A Secure Connection Or Client Was Not Authenticated

I have written the above code and im getting an error as below-System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at at

System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at smtptest._Default.btnSend_Click(Object sender, EventArgs e) in c:usersadministratordocumentsvisual studio 2010ProjectssmtptestsmtptestDefault.aspx.cs:line 71

Its working on local but when im hosting my application im getting above error

using (MailMessage mm = new MailMessage("myid@gmail.com","reciverid@yahoo.com"))
{
mm.Subject = "test";
mm.Body = "email testing";
mm.IsBodyHtml = false;
SmtpClient smtp = new SmtpClient();

[code]....