Connecting to smtp.live.com with the TcpClient cla

问题:

I'm trying to connect to smtp.live.com using the TcpClient class. There is a wonderful example of connecting to Gmail here: Testing SMTP server is running via C#

Unfortunately, when updating this to work with smtp.live.com, I'm getting an "IOException: The handshake failed due to an unexpected packet format" when the AuthenticateAsClient method is called.

How can I work around this?

class Program
{
    static void Main(string[] args)
    {
        using (var client = new TcpClient())
        {
            var server = "smtp.live.com";
            var port = 25;
            client.Connect(server, port);
            using (var stream = client.GetStream())
            using (var sslStream = new SslStream(stream))
            {
                // Getting an IOException here
                sslStream.AuthenticateAsClient(server);
                using (var writer = new StreamWriter(sslStream))
                using (var reader = new StreamReader(sslStream))
                {
                    writer.WriteLine("EHLO " + server);
                    writer.Flush();
                    Console.WriteLine(reader.ReadLine());
                }
            }
        }
        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();
    }
}

I tried specifying the SslProtocol in AuthenticateAsClient. Neither Tls or Ssl3 worked.

Also tried providing a callback for RemoteCertificateValidation that alway returned true just in case the server cert was invalid. That didn't work either.

NOTE: Please do not suggest that I use SmtpClient; I need more control than it provides.

回答1:

Thanks to nos for putting me on the right track. The smtp.live.com servers require the following sequence of events:

1. Connect
2. HELO - will not accept the STARTTLS until this has been sent
3. STARTTLS - apparently this sets up the server to accept an encrypted connection
4. SslStream.AuthenticateAsClient() - this seems to let the C# framework and the SMTP server come to an "understanding" :)
5. Now that we have an encrypted connection, the usual SMTP commands work

Anyway, this code works for both smtp.live.com AND smtp.gmail.com on port 587:

class Program
{
    static void Main(string[] args)
    {
        const string server = "smtp.live.com";
        const int port = 587;
        using (var client = new TcpClient(server, port))
        {
            using (var stream = client.GetStream())
            using (var clearTextReader = new StreamReader(stream))
            using (var clearTextWriter = new StreamWriter(stream) { AutoFlush = true })
            using (var sslStream = new SslStream(stream))
            {
                var connectResponse = clearTextReader.ReadLine();
                if (!connectResponse.StartsWith("220"))
                    throw new InvalidOperationException("SMTP Server did not respond to connection request");

                clearTextWriter.WriteLine("HELO");
                var helloResponse = clearTextReader.ReadLine();
                if (!helloResponse.StartsWith("250"))
                    throw new InvalidOperationException("SMTP Server did not respond to HELO request");

                clearTextWriter.WriteLine("STARTTLS");
                var startTlsResponse = clearTextReader.ReadLine();
                if (!startTlsResponse.StartsWith("220"))
                    throw new InvalidOperationException("SMTP Server did not respond to STARTTLS request");

                sslStream.AuthenticateAsClient(server);

                using (var reader = new StreamReader(sslStream))
                using (var writer = new StreamWriter(sslStream) { AutoFlush = true })
                {
                    writer.WriteLine("EHLO " + server);
                    Console.WriteLine(reader.ReadLine());
                }
            }
        }
        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();
    }
}

回答2:

If you want to use ssl on the connection. You should use port 465 for ssl or 587 for tls.

Tip: Try it first without ssl, and add it after you've got things working.

Link: http://www.checktls.com/tests.html to see some starttls examples.