The remote certificate is invalid according to the validation procedure

Question

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

User · Answer

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.

User · Answer

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

User · Answer

I had the same problem while I was testing a project and it turned that running Fiddler was the cause for this error      If you are using Fiddler to intercept the http request  shut it down      This is one of the many causes for such error   To fix Fiddler you may need to Reset Fiddler Https Certificates

User · Answer

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

User · Answer

You must check the certificate hash code   ServicePointManager ServerCertificateValidationCallback    sender  certificate  chain      errors    gt                        var hashString   certificate GetCertHashString                if  hashString    null                                var certHashString   hashString ToLower                    return certHashString     dec2b525ddeemma8ccfaa8df174455d6e38248c5                             return false

User · Answer

Try put this before send e-mail  ServicePointManager ServerCertificateValidationCallback            delegate object s  X509Certificate certificate  X509Chain chain          SslPolicyErrors sslPolicyErrors    return true       Remenber to add the using libs

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

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