Question

In the .NET framework there is a class TcpClient to retrieve emails from an email server. The TcpClient class has 4 constructors to connect with the server which take at most two parameters. It works fine with those servers which does not use SSL. But gmail or many other email providers use SSL for IMAP.

I can connect with gmail server but can not authenticate with email_id and password.

My code for authenticate user is

public void AuthenticateUser(string username, string password)
{
    _imapSw.WriteLine("$ LOGIN " + username + " " + password);
    //_imapSw is a object of StreamWriter class
    _imapSw.Flush();
    Response();
}

But this code can not login.

So how can I use the TcpClient class to retrieve emails when I have to use SSL?

Answer 1

You have to use the SslStream along with the TcpClient then use the SslStream to read the data rather than the TcpClient.

Something along the lines of:

        TcpClient mail = new TcpClient();
        SslStream sslStream;

        mail.Connect("pop.gmail.com", 995);
        sslStream = new SslStream(mail.GetStream());

        sslStream.AuthenticateAsClient("pop.gmail.com");

        byte[] buffer = new byte[2048];
        StringBuilder messageData = new StringBuilder();
        int bytes = -1;
        do
        {
            bytes = sslStream.Read(buffer, 0, buffer.Length);

            Decoder decoder = Encoding.UTF8.GetDecoder();
            char[] chars = new char[decoder.GetCharCount(buffer, 0, bytes)];
            decoder.GetChars(buffer, 0, bytes, chars, 0);
            messageData.Append(chars);

            if (messageData.ToString().IndexOf("<EOF>") != -1)
            {
                break;
            }
        } while (bytes != 0);

        Console.Write(messageData.ToString());
        Console.ReadKey();

EDIT

The above code will simply connect via SSL to Gmail and output the contents of a test message. To log in to a gmail account and issue commands you will need to do something along the lines of:

        TcpClient mail = new TcpClient();
        SslStream sslStream;
        int bytes = -1;

        mail.Connect("pop.gmail.com", 995);
        sslStream = new SslStream(mail.GetStream());

        sslStream.AuthenticateAsClient("pop.gmail.com");

        byte[] buffer = new byte[2048];
        // Read the stream to make sure we are connected
        bytes = sslStream.Read(buffer, 0, buffer.Length);
        Console.WriteLine(Encoding.ASCII.GetString(buffer, 0, bytes));

        //Send the users login details
        sslStream.Write(Encoding.ASCII.GetBytes("USER USER_EMAIL\r\n"));
        bytes = sslStream.Read(buffer, 0, buffer.Length);
        Console.WriteLine(Encoding.ASCII.GetString(buffer, 0, bytes));

        //Send the password                        
        sslStream.Write(Encoding.ASCII.GetBytes("PASS USER_PASSWORD\r\n"));
        bytes = sslStream.Read(buffer, 0, buffer.Length);
        Console.WriteLine(Encoding.ASCII.GetString(buffer, 0, bytes));

        // Get the first email 
        sslStream.Write(Encoding.ASCII.GetBytes("RETR 1\r\n"));
        bytes = sslStream.Read(buffer, 0, buffer.Length);
        Console.WriteLine(Encoding.ASCII.GetString(buffer, 0, bytes));

Obviously, without all the duplication of code 🙂