No connection could be made because the target machine actively refused it 127.0.0.1:25

[SocketException (0x274d): No connection could be made because the target machine actively refused it 127.0.0.1:25]
   System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) +208
   System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) +464

[WebException: Unable to connect to the remote server]
   System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object owner, Boolean async, IPAddress& address, Socket& abortSocket, Socket& abortSocket6) +6646520
   System.Net.PooledStream.Activate(Object owningObject, Boolean async, GeneralAsyncDelegate asyncCallback) +307
   System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback) +19
   System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout) +324
   System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint) +141
   System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint) +170
   System.Net.Mail.SmtpClient.GetConnection() +44
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1554

[SmtpException: Failure sending mail.]
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1906
   ContactUs.SendDetails() in d:\ClickPerks\ClickPerks\httpdocs\ContactUs.aspx.cs:48
   ContactUs.btnSubmit_Click(Object sender, EventArgs e) in d:\ClickPerks\ClickPerks\httpdocs\ContactUs.aspx.cs:54
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9628114
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +103
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724

private void SendDetails()
    {
        System.Text.StringBuilder oBuilder = new System.Text.StringBuilder();
        oBuilder.Append("Email=" + txtEmail.Text + Environment.NewLine);
        oBuilder.Append("Name=" + txtName.Text + Environment.NewLine);
        oBuilder.Append("Subject=" + txtSubject.Text + Environment.NewLine);
        oBuilder.Append("Message=" + txtDetails.Text);

        MailMessage oMM = new MailMessage();
        oMM.From = new MailAddress("info@clickperks.com");
        try
        {
            oMM.ReplyTo = new MailAddress("info@clickperks.com");
        }
        catch
        {
        }
        oMM.Subject = txtSubject.Text;
        oMM.Body = oBuilder.ToString();
        oMM.To.Add(ConfigurationManager.AppSettings.Get("ContactUsReceiverEmailID").ToString());
        SmtpClient client = new SmtpClient();
        client.Host = ConfigurationManager.AppSettings.Get("SMTPServerName").ToString();
        client.Send(oMM);
    }
    public void btnSubmit_Click(object sender, EventArgs e)
    {
        if (IsValid)
        {
            SendDetails();
            lblConfirmation.Text = "<br>Your details have been successfully submitted.  You should receive a response from us within two business days.<br>";
            txtEmail.Text = "";
            txtName.Text = "";
            txtSubject.Text = "";
            txtDetails.Text = "";

        }
    }

client.Send(oMM);