What happens to shared mailboxes during a tenant-to-tenant migration?
Shared mailboxes migrate with the same tooling as user mailboxes — content and the mailbox object move across. What doesn't come along automatically is the web of delegate permissions (Send As, Send on Behalf, Full Access) and distribution-group memberships pointing at them; those have to be inventoried before cutover and rebuilt in the target tenant, or users lose access the moment the mailbox lands.
What to inventory before cutover
- Every user or group with Send As, Send on Behalf, or Full Access on the shared mailbox.
- Distribution groups or Microsoft 365 Groups that include the shared mailbox as a member.
- Any mail flow rules or connectors that reference the shared mailbox's address specifically.
Read next
- Migrating a shared mailbox to a distribution group, or back— How to move an address from a shared mailbox to a distribution group, or back, without dropping mail — what happens to history, and when a Group is better.
- Microsoft 365 tenant-to-tenant migration— Migrating from one Microsoft 365 tenant to another — the workloads, the tools, and the realistic timeline.