Can I test SmtpClient before calling client.Send()?

Question

This is related to a question I asked the other day on how to send email.

My new, related question is this... what if the user of my application is behind a firew

Answer 1

I think that if you are looking to test the SMTP it's that you are looking for a way to validate your configuration and network availability without actually sending an email. Any way that's what I needed since there were no dummy email that would of made sense.

With the suggestion of my fellow developer I came up with this solution. A small helper class with the usage below. I used it at the OnStart event of a service that sends out emails.

Note: the credit for the TCP socket stuff goes to Peter A. Bromberg at http://www.eggheadcafe.com/articles/20030316.asp and the config read stuff to the guys here: Access system.net settings from app.config programmatically in C#

Helper:

public static class SmtpHelper
{
    /// 

    /// test the smtp connection by sending a HELO command
    /// 
    /// 
    /// 
    public static bool TestConnection(Configuration config)
    {
        MailSettingsSectionGroup mailSettings = config.GetSectionGroup("system.net/mailSettings") as MailSettingsSectionGroup;
        if (mailSettings == null)
        {
            throw new ConfigurationErrorsException("The system.net/mailSettings configuration section group could not be read.");
        }
        return TestConnection(mailSettings.Smtp.Network.Host, mailSettings.Smtp.Network.Port);
    }

    /// 

    /// test the smtp connection by sending a HELO command
    /// 
    /// 
    /// 
    public static bool TestConnection(string smtpServerAddress, int port)
    {
        IPHostEntry hostEntry = Dns.GetHostEntry(smtpServerAddress);
        IPEndPoint endPoint = new IPEndPoint(hostEntry.AddressList[0], port);
        using (Socket tcpSocket = new Socket(endPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp))
        {
            //try to connect and test the rsponse for code 220 = success
            tcpSocket.Connect(endPoint);
            if (!CheckResponse(tcpSocket, 220))
            {
                return false;
            }

            // send HELO and test the response for code 250 = proper response
            SendData(tcpSocket, string.Format("HELO {0}\r\n", Dns.GetHostName()));
            if (!CheckResponse(tcpSocket, 250))
            {
                return false;
            }

            // if we got here it's that we can connect to the smtp server
            return true;
        }
    }

    private static void SendData(Socket socket, string data)
    {
        byte[] dataArray = Encoding.ASCII.GetBytes(data);
        socket.Send(dataArray, 0, dataArray.Length, SocketFlags.None);
    }

    private static bool CheckResponse(Socket socket, int expectedCode)
    {
        while (socket.Available == 0)
        {
            System.Threading.Thread.Sleep(100);
        }
        byte[] responseArray = new byte[1024];
        socket.Receive(responseArray, 0, socket.Available, SocketFlags.None);
        string responseData = Encoding.ASCII.GetString(responseArray);
        int responseCode = Convert.ToInt32(responseData.Substring(0, 3));
        if (responseCode == expectedCode)
        {
            return true;
        }
        return false;
    }
}

Usage:

if (!SmtpHelper.TestConnection(ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)))
{
    throw new ApplicationException("The smtp connection test failed");
}