From email considered bad by server

[Guest.Visitor]

I am trying to write a C# code to send mail automatically (without using System.Web.Mail object)
//this is to START TLS
stdOut.WriteLine("STARTTLS");
stdOut.Flush();
responseCode = GetResponse(stdIn);
< stdOut.WriteLine("MAIL FROM:");
stdOut.Flush();
responseCode = GetResponse(stdIn);
But it is giving error because responseCode is 0
I am not able to figure out the problem One more thing is I am using My ISP's outgoing mail server for the same. If I don't issue STARTTLS command it throws exception as 'Must issue STARTTLS command. Thanks in advance!!