You bought the practice. Their logins don't come with it.

Microsoft's own tooling for merging two Microsoft 365 tenants moves your content. It does not move your people.

That surprises almost every practice owner I talk to who is about to add a second location.

Here is what actually happens when you acquire another practice. You now own two completely separate environments. Two sets of accounts, two sets of security rules, two mailboxes for the office manager who suddenly works across both. Everyone assumes the IT side is a weekend job. It isn't.

Microsoft is explicit about it: before a single email or file moves, every user has to be created in the destination tenant and mapped one to one. Those destination accounts also have to be clean — if someone already has a mailbox sitting there, their migration fails.

Get that order wrong and you are untangling it during your first month owning the place. Front desk can't see the schedule. Patient messages bounce. Staff start routing work through personal email because it's the only thing that works.

That is real money, in the exact month you need collections to be cleanest.

So if a second location is on the whiteboard for next year, sort the identity side before you sign, not after. It's a planning conversation, not an emergency one.