sending mail works on server but not on my local machine

Question

i have the following code below (i have stuck in xxx to not publish the real name). this code works fine when i upload to the server and will send out emails perfectly.

        MailMessage msg = new MailMessage();
        msg.From = new MailAddress(fromEmailAddress_);
        msg.To.Add(new MailAddress(toEmailAddress_));

        msg.Subject = subject_;
        msg.Body = body_;
        msg.IsBodyHtml = true;
        msg.Priority = MailPriority.High;

        NetworkCredential basicAuthenticationInfo = new System.Net.NetworkCredential("[email protected]", "password");
        try
        {
            SmtpClient c = new SmtpClient("mail.xxx.org");
            c.UseDefaultCredentials = false;
            c.Credentials = basicAuthenticationInfo;
            c.Send(msg);
        }
        catch (Exception ex)
        {
            throw ex;
            Console.Write(ex.Message.ToString());
        }

but when i test locally on my machine in visual studio, i get an error:

[SocketException (0x274d): No connection could be made because the target machine actively refused it 66.226.21.251:25] System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) +239 System.Net.Sockets.Socket.InternalConnect(EndPoint remoteEP) +35 System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception) +224

[WebException: Unable to connect to the remote server] System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object owner, Boolean async, IPAddress& address, Socket& abortSocket, Socket& abortSocket6, Int32 timeout) +5420699 System.Net.PooledStream.Activate(Object owningObject, Boolean async, Int32 timeout, GeneralAsyncDelegate asyncCallback) +202 System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback) +21 System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout) +332 System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port) +160 System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port) +159

any suggestions of why this wouldn't work

William Pietri William Pietri · Accepted Answer · 2009-08-06T06:04:46

The first thing I'd do to run this down is to see whether the target machine is, as the error message says, actually refusing the connections. I can connect to port 25 on that IP address from here, so it's possible that your error message is misleading. These are all possible causes of a failure to connect:

there's some problem in your code
there's some problem in the library you're using
you have a local firewall preventing outbound mail from strange programs
your ISP does not permit outbound SMTP connections except to their own servers
some intermediate network is blocking things
the mail server's ISP is blocking SMTP connections from your network
the mail server really is rejecting you, perhaps because you're on a blocklist

To get more detail, download and install Wireshark. It's like a debugger for networks. Start a capture between your system and the target network and then run your code. Interpreting the captured packets takes some experience, so if you get stuck feel free to post more data here.

sending mail works on server but not on my local machine

6 Answers