So, if I understand correctly, this applies to a single PM being sent to many users at the same time, meaning if my llimit is 3 max PM recipients, I only send one PM to not more than 3 users simultaneously? But I can send PMs to as many users as I want, provided each single PM isn't being sent to more than 3? Or have I misunderstood you?
Nope, that's exactly how it works.
You can send each PM to a maximum of X users (3 for your rank, didn't check back, but I take your word on that).
You can then (after your PM/post cooldown) send another PM to either the same, or 3 different users, and so on.