C # Use the POP3 Protocol to implement SSL authentication and log on to Gmail

Recently, with the POP3 protocol, logging on to pop.qq.com and pop.163.com is no problem, so I thought about logging on to pop.gmail.com and the result failed. After investigation, we found that Gmail's POP3 port is not 110, but 995. So I changed the port, but the login still failed. After checking the information, we found that Gmail used SSL verification and cannot connect directly. Then how does C # implement SSL connections? After checking a lot of information, we found that it can be implemented through sslstream.

The following is the connection code of sslstream.

  private StreamReader pop3StreamReader_ = null;        private SslStream pop3Stream_ = null;              public void connect(string host, int port)        {            try            {                TcpClient popServer = new TcpClient(host, port);                pop3Stream_ = new SslStream(popServer.GetStream(), false);                pop3Stream_.AuthenticateAsClient(host);                isConnected_pro = true;                pop3StreamReader_ = new StreamReader(pop3Stream_, encoding_pro);                            }            catch (System.Exception ex)            {                exception_pro = ex;                isConnected_pro = false;            }        }

Pop3streamreader _ is used to receive response data.

How do I send data after the SSL connection is successful? You can use the write method of sslstream. The following describes how to send data.

   public bool send(string sendStr)        {            try            {                exception_pro = null;                pop3Stream_.Write(encoding_pro.GetBytes(sendStr));                return true;            }            catch (System.Exception ex)            {                exception_pro = ex;                return false;            }        }

How can I receive the data? You can use the Readline method of pop3streamreader.
The following describes how to receive data.

/// <summary>        /// Receive one line data.        /// </summary>        /// <returns></returns>        public string receive()        {            string receiveStr = "";            receiveStr = pop3StreamReader_.ReadLine();            return receiveStr;        }

Below is a simple call to the above method

  private void buttonSsl_Click(object sender, EventArgs e)        {            SslSp sslSp = new SslSp();            sslSp.connect("pop.gmail.com", 995);            string receiveStr = sslSp.receive();            MessageBox.Show(receiveStr);            sslSp.send("user mysuer\r\n");            receiveStr = sslSp.receive();            MessageBox.Show(receiveStr);            sslSp.send("pass mypassword\r\n");            receiveStr = sslSp.receive();            MessageBox.Show(receiveStr);}

In actual applications, we recommend that you add a disconnect function for SSL connections to facilitate management.