i can not connect the mail server of yahoo on port 25

Question

A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 67.195.204.77:25

this is my code
TcpClient tclient = new TcpClient();
tclient.Connect(emailserverip,25);
Label4.Text = "server is connected ";
string CRLF = "\r\n";
byte[] dataBuffer;
string ResponseString;

                                NetworkStream netstream = tclient.GetStream();
                                StreamReader sr = new StreamReader(netstream);
                                ResponseString = sr.ReadLine();

                                /* Perform HELO to SMTP Server and get Response */
                                dataBuffer = BytesFromString("HELO" + CRLF);
                                netstream.Write(dataBuffer, 0, dataBuffer.Length);
                                ResponseString = sr.ReadLine();
                                //sender mail 
                                dataBuffer = BytesFromString("MAIL FROM:<Check@" + host + ">" + CRLF);
                                netstream.Write(dataBuffer, 0, dataBuffer.Length);
                                ResponseString = reader.ReadLine();
                                /* Read Response of the RCPT TO Message to know mailbox if it exist or not */
                                dataBuffer = BytesFromString("RCPT TO:<" + email + ">" + CRLF);
                                netstream.Write(dataBuffer, 0, dataBuffer.Length);
                                ResponseString = reader.ReadLine();
                                if (GetResponseCode(ResponseString) == 550)
                                {
                                    continue;
                                }
                                else
                                {
                                  Label5.Text = "GOOD";

                                }
                                /* QUITE CONNECTION */
                                dataBuffer = BytesFromString("QUITE" + CRLF);
                                netstream.Write(dataBuffer, 0, dataBuffer.Length);
                                tclient.Close();