在Orchard CMS提交表單時無法發送電子郵件

我使用Orchard 1.10.1。提交包含發送電子郵件活動的表單後，我在AppData/Logs中收到此錯誤。在Orchard CMS提交表單時無法發送電子郵件

2016-12-01 10:39:07,242 [11] Orchard.Email.Services.SmtpMessageChannel - 
Default - Could not send email [http://yxyxyx.com/Orchard.DynamicForms/Form/Submit] 
System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A socket operation was attempted to an unreachable network [2a00:1450:400c:c04::6d]:587 
    at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) 
    at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) 
    --- End of inner exception stack trace --- 
    at System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object owner, Boolean async, IPAddress& address, Socket& abortSocket, Socket& abortSocket6) 
    at System.Net.PooledStream.Activate(Object owningObject, Boolean async, GeneralAsyncDelegate asyncCallback) 
    at System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback) 
    at System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout) 
    at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint) 
    at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint) 
    at System.Net.Mail.SmtpClient.GetConnection() 
    at System.Net.Mail.SmtpClient.Send(MailMessage message) 
    --- End of inner exception stack trace --- 
    at System.Net.Mail.SmtpClient.Send(MailMessage message) 
    at Orchard.Email.Services.SmtpMessageChannel.Process(IDictionary`2 parameters)

我應該如何解決這個問題？

---------更新---------

在配置中測試發送電子郵件失敗。這是我的配置：