The remote certificate is invalid according to the validation procedure

Hi, i'm currently using 8.1.3, and i'm facing this error while sending a mail.


(2022-06-20 12:58:22.900) [System.Security.Authentication.AuthenticationException] The remote certificate is invalid according to the validation procedure.
at StdioProcessor.StdioProcessor._Execute(Job job)
at VI.JobService.JobComponents.MailComponent.Activate(String task)
at VI.JobService.JobComponents.MailComponent._SendRichMail()
at VI.JobService.JobComponents.MailComponent._Send(MimeMessage message, MailSecurity security)
at VI.JobService.JobComponents.MailComponent._GetOrOpenSmtpConnection()
at MailKit.Net.Smtp.SmtpClient.Connect(String host, Int32 port, SecureSocketOptions options, CancellationToken cancellationToken)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, Exception exception)


About this error the strange thing is that up to 3 days ago it worked and no changes have been made from that day to today.

I've already tried the solutions suggested in these posts but they didn't work:
www.oneidentity.com/.../the-remote-certificate-is-invalid-according-to-the-validation-procedure
www.oneidentity.com/.../invalid-error-in-certificate

Thanks in advance,

Giorgio.