Per-seat economics, granular restore, retention policy, and bring-your-own-storage.
Per-user rates are the easy part. The bill is made of the four things vendors don’t put on the landing page.
The covered list is marketing. The not-covered list is where your restore fails
The vendor is not party to your storage contract, which is the whole point
Microsoft keeps the service running. Protecting the data inside it is your job — and that split is written into the agreement.
Recycle bins and retention policies keep data for a while. A backup is a separate copy you control — and the difference shows up during a restore.
An 8-hour window on a 200-seat tenant is roughly 8,000 unrecoverable messages
A 500-seat client at 8% churn carries 280 departed users by year seven
Model the offboarding case, not the growth case
Four numbers, no spreadsheet, no call to the vendor
