The remote certificate is invalid according to the validation procedure [duplicate]

Running the following code, I get an exception:

using (var client = new Pop3Client())
{
    client.Connect(provider.ServerWithoutPort, provider.Port, true);
}

The Exception I get:

The remote certificate is invalid according to the validation procedure.


   at System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, Exception exception)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Net.Security.SslStream.AuthenticateAsClient(String targetHost, X509CertificateCollection clientCertificates, SslProtocols enabledSslProtocols, Boolean checkCertificateRevocation)
   at System.Net.Security.SslStream.AuthenticateAsClient(String targetHost)
   at OpenPop.Pop3.Pop3Client.Connect(String hostname, Int32 port, Boolean useSsl, Int32 receiveTimeout, Int32 sendTimeout, RemoteCertificateValidationCallback certificateValidator)
   at OpenPop.Pop3.Pop3Client.Connect(String hostname, Int32 port, Boolean useSsl)
   at Ugi.Server.Sources.Logic.SourcesService.IsValidPop3Connection(String email, String emailPassword) in C:\Users\elad\Documents\Visual Studio 2010\Projects\SVN\UGI\Ugi\Server\Sources\Logic\SourcesService.cs:line 246

Solution 1:

This usually occurs because either of the following are true:

• The certificate is self-signed and not added as a trusted certificate.
• The certificate is expired.
• The certificate is signed by a root certificate that's not installed on your machine.
• The certificate is signed using the fully qualified domain address of the server. Meaning: cannot use "xyzServerName" but instead must use "xyzServerName.ad.state.fl.us" because that's basically the server name as far as the SSL cert is concerned.
• A revocation list is probed, but cannot be found/used.
• The certificate is signed via intermediate CA certificate and server does not serve that intermediate certificate along with host certificate.

Try getting some information about the certificate of the server and see if you need to install any specific certs on your client to get it to work.

Solution 2:

Even shorter version of the solution from Dominic Zukiewicz:

ServicePointManager.ServerCertificateValidationCallback += (o, c, ch, er) => true;

But this means that you will trust all certificates. For a service that isn't just run locally, something a bit smarter will be needed. In the first instance you could use this code to just test whether it solves your problem.

Solution 3:

.NET is seeing an invalid SSL certificate on the other end of the connection. There is a workaround for it, but obviously not recommended for production code:

// Put this somewhere that is only once - like an initialization method
ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(ValidateCertificate);
...

static bool ValidateCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
{
   return true;
}