We are currently using Office 365 for education in one of our forest which contains a AD, master of the domain (example.com), a AD "sub-domain" (test.example.com), another AD (examplebis.com) and a DirSyn which works perfectly.
My point here is about the limitation of 50.000 objects that can be supported by O365. I understand that is for the entire forest, no problem with that.
But I've been asked: "Is it also concern the deleted objects ?". I mean here: if i create then delete a user in my O365 account, do I have 50.000 accounts left or 49.999 ?
I've not found an explicit answer in documentation, and even if my question could seem stupid, I prefer asking than giving a uncertain answer.