.net 跳支付宝接口时发生错误，各位高手帮忙看看

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Server Error in '/' Application.
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由于目标机器积极拒绝，无法连接。 123.125.50.133:25 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Net.Sockets.SocketException: 由于目标机器积极拒绝，无法连接。 123.125.50.133:25

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace: 


[SocketException (0x274d): 由于目标机器积极拒绝，无法连接。 123.125.50.133:25]
   System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) +225
   System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception) +279

[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) +6054772
   System.Net.PooledStream.Activate(Object owningObject, Boolean async, Int32 timeout, GeneralAsyncDelegate asyncCallback) +314
   System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback) +21
   System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout) +322
   System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint) +146
   System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint) +170
   System.Net.Mail.SmtpClient.GetConnection() +50
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1484

[SmtpException: Failure sending mail.]
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1811
   Comment.emailTool.mail_cend(String email_address, String sendAddress, String sendPassword, String email_text, String title, String host) in F:\vocoso\Comment\emailTool.cs:40
   Web.payList.Button3_Click(Object sender, EventArgs e) in F:\vocoso\Web\payList.aspx.cs:377
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
   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) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563