SMTP "An error occurred while attempting to establish an SSL or TLS connection"

Hi all, my Send SMTP activity just stopped working as of a few days ago. It was previously working just fine. It looks like some sort of patch or update came through for UIPath (my studio looks different) and maybe that’s what caused it to stop working?

FYI I am using company domain, not Gmail. Enterprise edition 2019.4.4. The servers we are using can send SMTP using cmd just fine.

Here is the error I am getting:
19.4.4+Branch.support/v2019.4.Sha.6d308c7f5a32b559373887ae421ce7eaec8f8d24

Source: Send SMTP Mail Message

Message: An error occurred while attempting to establish an SSL or TLS connection.

The SSL certificate presented by the server is not trusted by the system for one or more of the following reasons:

  1. The server is using a self-signed certificate which cannot be verified.
  2. The local system is missing a Root or Intermediate certificate needed to verify the server’s certificate.
  3. The certificate presented by the server is expired or invalid.

See https://github.com/jstedfast/MailKit/blob/master/FAQ.md#InvalidSslCertificate for possible solutions.

Exception Type: MailKit.Security.SslHandshakeException

An ExceptionDetail, likely created by IncludeExceptionDetailInFaults=true, whose value is:
MailKit.Security.SslHandshakeException: An error occurred while attempting to establish an SSL or TLS connection.

The SSL certificate presented by the server is not trusted by the system for one or more of the following reasons:

  1. The server is using a self-signed certificate which cannot be verified.
  2. The local system is missing a Root or Intermediate certificate needed to verify the server’s certificate.
  3. The certificate presented by the server is expired or invalid.

See https://github.com/jstedfast/MailKit/blob/master/FAQ.md#InvalidSslCertificate for possible solutions. ----> System.Security.Authentication.AuthenticationException: 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.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 MailKit.Net.Smtp.SmtpClient.d__70.MoveNext()
— End of inner ExceptionDetail stack trace —
at UiPath.Mail.Activities.SendMailActivity.EndExecute(AsyncCodeActivityContext context, IAsyncResult result)
at System.Activities.AsyncCodeActivity.System.Activities.IAsyncCodeActivity.FinishExecution(AsyncCodeActivityContext context, IAsyncResult result)
at System.Activities.AsyncCodeActivity.CompleteAsyncCodeActivityData.CompleteAsyncCodeActivityWorkItem.Execute(ActivityExecutor executor, BookmarkManager bookmarkManager)

We figured out it was an expired SSL certificate on a mail exchange server.

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