Perhaps it would be good to apply some sort of penalty to accounts that stop interacting for a long time (years), i.e., lower their rank.
No, it will be wrong to do so. Some accounts dont interact in the forum because of some certain reasons but once in a while they visis the forum. You cannot tell why they were absent so reducing the rank is not a good option. BlackHatCoiner said goodbye to the forum in
December 2023 but he was last active in February 2025. Scamvirus was inactive for more than 6 months, now he is
active againSince sometimes it can be difficult to tell if it's the same person starting to post again or not.
It is very simple to tell. Let them sign or verify the previous address that was used in the forum. And if vigilant members of the forum figure out difference in posting style they will notify everyone. Dont worry about that.