The current version runs fine on R6.5 and R7 (which are used by everyone I've had to directly support so far), and I have not tested it on R8.
If there is a different, the only thing that should matter is the mail import, which should be fairly simple to adjust.
I am developing on R6.5. I have no plans to move my own systems forward until R8.5. (things have been moving a little too fast in the Lotus world to play constant catch-up.)