Hello 365 admins, I have a peculiar need that I can't seem to find any reference for. A little background first.
We have the Office 365 Non-Profit E1 plan. Since we're an after school-based program, my user-base fluctuates between 400-600 users depending on time of year, with summer being the busiest. A majority of users are part-time workers that do not have dedicated workstations, but still require access to email and organizational resources for communication.
That being said, some of these users quit and return to help during the busier times of year - like holidays and summer - to work with our students. I understand that Exchange Online will only hold an unlicensed user's mailbox for so long before being permanently deleted (correct me if I'm wrong).
With on-prem Exchange, this wasn't as issue, as we'd backup the user's PST to...