Have a client with Domino 9 and 8.5.3 clients. Using the 8.5 Mail Template. I have ONE user who at some unknown time mail filtering rules stopped working. Upon inspection of the inbox rules, the Tools->Rules option is missing. All that shows up under Tools is Stationary.
Compacted the DB, Refreshed design, Replaced Design, fixup all did nothing to show the rules option again. Everything else appears to work fine. Other users rules show and work fine as well.