The problem with sending mail

Question

Hi all.
i am uisng visual studio 2003 to create simple web for sending mail base on the smtp server like that :
 

 

string smtpServer = "smtp.gmail.com";

string userName = "metilmarket";

string password = "i5kngyvx";

int cdoBasic = 1; 

int cdoSendUsingPort = 2; 

MailMessage msg = new MailMessage(); 

if (userName.Length > 0) 

{

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserver", smtpServer); 

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserverport", 25);

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusing", cdoSendUsingPort); 

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", cdoBasic);

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", userName); 

msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", password); 

} 

msg.To = "[email protected]";

msg.From = "[email protected]";

msg.Subject = "Subject";

msg.Body = "Message";

SmtpMail.SmtpServer = smtpServer;

SmtpMail.Send(msg);

lb1mgs.Text = "Your message has been successfully sent.";

But i am get error when i do the transaction with smtp :
errors like that :
The server rejected the sender address. The server response was: 530 5.7.0 Must issue a STARTTLS command  first. n35sm3933492wfa.15
 i am using gmail to test this application.
 Please give me suggestion , how to correct it ?
 
thanks in advances.