I think it might be a good idea to add a “inactive user” icon or notification next to a member’s profile (so you can see it when they post - maybe below their joined date). That way if a member of Forumosa reads an interesting post by another Forumosa member who has not logged in to Forumosa in 5 years or so, they don’t make the mistake of PMing that inactive user or asking them a direct question on the forum and expecting an answer.
Does that sound reasonable?