Setting up an testing our shiny new server and Free SM16.x build  (whatever the current one is)....

Interfacing, or attempting to interface to outbound SM15.x gateway...

Receive this error:

16:28:30.730 [26000] Exception: The handshake failed due to an unexpected packet format.
   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.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   at MailService.RelayServer.Clients.SMTP.ClientConnectionSync.InitiateSsl(Boolean validateAllCerts)
   at MailService.RelayServer.Clients.SMTP.SmtpClientSession.Initialize(String senderAddress, List`1 recipientList, String destServerIP)
~~~

Not sure what that means, or what I need to do resolve.

The current outbound gate-way is being used by the prod box as well.. so new test server and prod server using the same outbound gateway.. Is that the problem?