ohh ok.. I just thought the other way made more sense since user2 sent the message "to" user1. so saving it as "user2:to:user1" instead of "user1:to:user2" was more intuitive. sorry
Didn't work postcount for sub category & didn't work preview
In v.0.7.1 & v.0.7.2 correctly count posts in old structure of sub category.
But if create new category & create post in sub category - counter didn't "see" posts in subcategory & didn't preview posts in main page.
Bug report in git - https://github.com/NodeBB/NodeBB/issues/3368