About the MX Record Entry of hotmail,yahoomail & Rediffmail

I am designing one web page which checks the existence of the Email Address on the server

For that I have the following code.....this code checks the the existence of gmail address for

e.g [email protected] on the Gmail server

so can anyone please tell me what is the MX Record Entry of Hotmail,Yahoomail and Rediffmail provider.

 TcpClient tClient = new TcpClient("gmail-smtp-in.l.google.com", 25); 

string CRLF = "\r\n";

 byte[] dataBuffer;

 string ResponseString;

 NetworkStream netStream = tClient.GetStream();

 StreamReader reader = new StreamReader(netStream);

ResponseString = reader.ReadLine(); 

/* Perform HELO to SMTP Server and get Response */     

 dataBuffer = BytesFromString("HELO KirtanHere" + CRLF);    

  netStream.Write(dataBuffer, 0, dataBuffer.Length);

 ResponseString = reader.ReadLine();  

   dataBuffer = BytesFromString("MAIL FROM:" + CRLF);   

   netStream.Write(dataBuffer, 0, dataBuffer.Length);

 ResponseString = reader.ReadLine();

 /* Read Response of the RCPT TO Message to know from google if it exist or not */   

   dataBuffer = BytesFromString("RCPT TO:<"+TextBox1.Text.Trim()+">"+CRLF);   

   netStream.Write(dataBuffer, 0, dataBuffer.Length); 

ResponseString = reader.ReadLine(); if (GetResponseCode(ResponseString) == 550) { Label1.Visible = true; Label1.Text = "Mai Address Does not Exist !";

 Label1.Text = "Original Error from Smtp Server :" + ResponseString; 

//Response.Write("Mai Address Does not Exist !

"); 

//Response.Write("Original Error from Smtp Server :" + ResponseString); 

} 

else { Label1.Visible = true; 

Label1.Text = "exist"; 

//Response.Write("valid address");

 } /* QUITE CONNECTION */  

    dataBuffer = BytesFromString("QUITE" + CRLF);   

   netStream.Write(dataBuffer, 0, dataBuffer.Length);  

    tClient.Close();

 } private byte[] BytesFromString(string str)

 { return Encoding.ASCII.GetBytes(str); } private int GetResponseCode(string ResponseString)

 { return int.Parse(ResponseString.Substring(0, 3)); }