Up to now, i keep the Lotus Notes As inbound SMTP gateway.
The downside is that all icoming mail on Exchange are tagged with @NOTEDOMAIN at the end.
The MS KB 255160 indicate that it's recommanded to set the Exchange as smtp inbound gateway.
I tried it, but then i got all mail to Lotus users kept for 10 minutes in the exchange queue. They stay in the deferred delivery queue without any reason.
I will update this post when resolved
-I turned again the Exchange as the inbound smtp gateway. It works ! I changed many things, so i don't really know the guilty parameter.
The Exchange is now also the SMTP outbound for the Lotus Notes. @SMTP@Exchange mail were tagged since, but i applied the MS KB 251955. The suffix is gone, and mail flows work much better!