EmailPlus SSL error

[bbeardqrails]

I'm getting an error trying to send an email alert using the Seq.App.EmailPlus (v3.1.0-dev-00179) app, Seq 2021.2.5647. Our SMTP server is on port 25 and I do not have the checkbox checked to "Require TLS". Yet I'm getting the following error when trying to send a an email:

MailKit.Security.SslHandshakeException: An error occurred while attempting to establish an SSL or TLS connection.

The server's SSL certificate could not be validated for the following reasons:
• The server certificate has the following errors:
  • A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file.
  • The revocation function was unable to check revocation for the certificate.
  • The revocation function was unable to check revocation because the revocation server was offline.
• An intermediate certificate has the following errors:
  • The revocation function was unable to check revocation for the certificate.
  • The revocation function was unable to check revocation because the revocation server was offline.

 ---> System.Security.Authentication.AuthenticationException: The remote certificate was rejected by the provided RemoteCertificateValidationCallback.
   at System.Net.Security.SslStream.SendAuthResetSignal(ProtocolToken message, ExceptionDispatchInfo exception)
   at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](TIOAdapter adapter, Boolean receiveFirst, Byte[] reAuthenticationData, Boolean isApm)
   at MailKit.Net.Smtp.SmtpClient.ConnectAsync(String host, Int32 port, SecureSocketOptions options, Boolean doAsync, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at MailKit.Net.Smtp.SmtpClient.ConnectAsync(String host, Int32 port, SecureSocketOptions options, Boolean doAsync, CancellationToken cancellationToken)
   at Seq.App.EmailPlus.DirectMailGateway.SendAsync(SmtpOptions options, MimeMessage message) in C:\projects\seq-app-htmlemail\src\Seq.App.EmailPlus\DirectMailGateway.cs:line 16
   at Seq.App.EmailPlus.EmailApp.OnAsync(Event`1 evt) in C:\projects\seq-app-htmlemail\src\Seq.App.EmailPlus\EmailApp.cs:line 147
   at SeqCli.Apps.Hosting.AppContainer.SendTypedEventAsync(String clef) in C:\projects\seqcli\src\SeqCli\Apps\Hosting\AppContainer.cs:line 113```

[MattMofDoom]

Hi @bbeardqrails,

This is a bit of an issue relating to how the MailKit SMTP TLS validation works by default, with standard .NET certificate validation. There are workarounds for certificate validation such as installing the certificate as trusted on the Seq server, but I have had challenges getting that to work in some cases.

There is a pull request in progress for Email+ which provides a full dropdown list of TLS behaviours. This includes the "None" option which will definitively turn off TLS.

While the pull request is still pending review, I have published a dev version that includes all enhancements at https://www.nuget.org/packages/Seq.App.EmailPlus-Enhanced

Hope that's of assistance for your case.

Cheers,

Matt

[bbeardqrails]

Thanks. We were able to fix the issue by setting up the cert properly on the box.