OnlyBusy
Block time across separate Microsoft 365 tenants
Last updated 3 October 2026
Each Microsoft 365 tenant keeps its own free/busy. A meeting inside one client does not appear on the next client's calendar, so Scheduling Assistant there still offers the hour. A private Busy event written into each tenant is what those tools can see.
One tenant cannot see another tenant's events
Client A's directory and client B's directory are separate. An event in one is not an event in the other, even when you are the same person on both.
Scheduling Assistant in B offers the hour unless B's calendar has its own Busy event.
What personal consent can connect
You sign in to each Microsoft 365 account the way you sign in to any calendar app. That consent lets OnlyBusy write the Busy event into that tenant.
Google Calendar accounts connect the same way, including Workspace.
When a tenant blocks user consent
Some tenants disable user consent for third-party apps. That calendar cannot be connected until an admin allows consent for it.
OnlyBusy does not request a tenant-wide admin install to get around that block.
A different label per calendar
Each destination can show a different label. One tenant can read External commitment. Another can read Busy.
The label is the whole of what that tenant receives. The other client's name is not in it.
What disconnect removes
Disconnect a calendar and OnlyBusy deletes the Busy events it created on that calendar, stops listening, and deletes the stored tokens for that account.
Events you created yourself stay. Only the blocks OnlyBusy wrote are removed.
Questions
How do I block time on two Microsoft 365 tenants?
Connect both accounts with personal sign-in. OnlyBusy writes a private Busy event into each one when the other calendar has a conflicting event.
What if the client blocks third-party apps?
That calendar cannot be connected until an admin allows user consent. OnlyBusy does not ask you to install a tenant-wide app.
Can each client see a different label?
Yes. You choose the label per calendar. They still do not see the title, guests, notes, or location from the other meeting.