mgb
db domains setprop my.mail.sme.com MailServer 192.168.183.17
signal-event email-update
When you do that, ALL mail for my.mail.sme.com is delegated to the exchange server.
user17@my.Exchange.local
Instead try
user17@my.mail.sme.com
I edited my earlier post, you may have missed seeing this additional suggestion:
Maybe even create another VALID domain on your sme that is delegated to the exchange server, just for those users who need to use exchange ie
user17@yourdomain2.com
and do
db domains setprop yourdomain2.com MailServer 192.168.183.17
signal-event email-update
You would also need to create valid external DNS records for yourdomain2.com