The Remote Certificate is invalid according to the Validation Procedure using Gmail SMTP Server : #
I’m getting this error:
The remote certificate is invalid according to the validation procedure.
whenever I try to send e-mail using Gmail’s SMTP server in my C# code. Can someone point me to the right direction for a solution to this problem?
The following is the stack trace…
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.TlsStream.CallProcessAuthentication(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.Mail.SmtpConnection.Flush()
at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
at System.Net.Mail.SmtpClient.GetConnection()
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at BulkEmail.frmemail.mailsending(String toaddress, String fromaddress, String fromname, String subject, String pwd, String attachements, String mailmessage, String htmlmessage, Int32 i, Int32 j, String replytoaddress)
Here is Some Solutions :
Solution 1: #
As a workaround, you can switch off certificate validation. Only ever do this to obtain confirmation that the error is being thrown because of a bad certificate.
Call this method before you call smtpclient.Send():
[Obsolete(“Do not use this in Production code!!!”,true)]
static void NEVER_EAT_POISON_Disable_CertificateValidation()
{
// Disabling certificate validation can expose you to a man-in-the-middle attack
// which may allow your encrypted message to be read by an attacker
// https://stackoverflow.com/a/14907718/740639
ServicePointManager.ServerCertificateValidationCallback =
delegate (
object s,
X509Certificate certificate,
X509Chain chain,
SslPolicyErrors sslPolicyErrors
) {
return true;
};
}
Solution 2: #
private static bool CertificateValidationCallBack(
object sender,
System.Security.Cryptography.X509Certificates.X509Certificate certificate,
System.Security.Cryptography.X509Certificates.X509Chain chain,
System.Net.Security.SslPolicyErrors sslPolicyErrors)
{
// If the certificate is a valid, signed certificate, return true.
if (sslPolicyErrors == System.Net.Security.SslPolicyErrors.None)
{
return true;
}
// If there are errors in the certificate chain, look at each error to determine the cause.
if ((sslPolicyErrors & System.Net.Security.SslPolicyErrors.RemoteCertificateChainErrors) != 0)
{
if (chain != null && chain.ChainStatus != null)
{
foreach (System.Security.Cryptography.X509Certificates.X509ChainStatus status in chain.ChainStatus)
{
if ((certificate.Subject == certificate.Issuer) &&
(status.Status == System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.UntrustedRoot))
{
// Self-signed certificates with an untrusted root are valid.
continue;
}
else
{
if (status.Status != System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.NoError)
{
// If there are any other errors in the certificate chain, the certificate is invalid,
// so the method returns false.
return false;
}
}
}
}
// When processing reaches this line, the only errors in the certificate chain are
// untrusted root errors for self-signed certificates. These certificates are valid
// for default Exchange server installations, so return true.
return true;
}
else
{
// In all other cases, return false.
return false;
}
}
Solution 3: #
<?xml version=”1.0″ encoding=”utf-8″ ?>
<configuration>
<system.diagnostics>
<trace autoflush=”true” />
<sharedListeners>
<add name=”file” initializeData=”c:\network.log” type=”System.Diagnostics.TextWriterTraceListener” />
</sharedListeners>
<sources>
<source name=”System.Net” switchValue=”Verbose”>
<listeners>
<add name=”file” />
</listeners>
</source>
</sources>
</system.diagnostics>
</configuration>
Rerun your application and check the c:\network.log file. You should see there detailed information about your TLS (SSL) connection, for example:
System.Net Information: 0 : [12764] InitializeSecurityContext(credential = System.Net.SafeFreeCredential_SECURITY, context = f44368:535f958, targetName = localhost, inFlags = ReplayDetect, SequenceDetect, Confidentiality, AllocateMemory, InitManualCredValidation)
System.Net Information: 0 : [12764] InitializeSecurityContext(In-Buffers count=2, Out-Buffer length=0, returned code=OK).
System.Net Information: 0 : [12764] Remote certificate: [Version]
V3
[Subject]
CN=test
Simple Name: test
DNS Name: example.com
[Issuer]
CN=Root CA
Simple Name: Root CA
DNS Name: Root CA
…
[Signature Algorithm]
sha256RSA(1.2.840.113549.1.1.11)
[Public Key]
Algorithm: RSA
Length: 2048
Key Blob: ….
System.Net Information: 0 : [12764] SecureChannel#38496415 – Remote certificate has errors:
System.Net Information: 0 : [12764] SecureChannel#38496415 – Certificate name mismatch.
System.Net Information: 0 : [12764] SecureChannel#38496415 – Remote certificate was verified as invalid by the user.
System.Net Error: 0 : [12764] Exception in AppDomain#10923418::UnhandledExceptionHandler – The remote certificate is invalid according to the validation procedure..
Solution 4: #
private void sendAMail(String toAddress, String messageBody)
{
String msg = “Sending mail to : ” + toAddress;
MailMessage mail = new MailMessage();
mail.To.Add(toAddress);
mail.From = new MailAddress(“from@mydomain.com”);
mail.Subject = “Subject: Test Mail”;
mail.Body = messageBody;
mail.IsBodyHtml = true;
//Added this line here
System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(RemoteServerCertificateValidationCallback);
SmtpClient smtp = new SmtpClient();
smtp.Host = “myhostname.com”;
smtp.Credentials = new System.Net.NetworkCredential(“sender@sample.com”, “”);
smtp.EnableSsl = true;
smtp.Port = 587;
smtp.Send(mail);
}
private bool RemoteServerCertificateValidationCallback(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors sslPolicyErrors)
{
//Console.WriteLine(certificate);
return true;
}
