Shared mailbox vs group mailbox decision guide
Overview
Teams often debate shared mailbox (Exchange) vs Microsoft 365 Group / Team for “department@”. Criteria below reduce rework.
Use a shared mailbox when
- Primarily email with delegated Send As/Send on Behalf.
- No need for shared SharePoint site or Planner by default.
- You want mailbox under 50 GB without tying to a user license (with correct configuration).
Use a group / Team when
- Collaboration needs files, chat, and channels alongside email.
- Cross-functional projects with guest access requirements.
- Modern compliance labels must span email + files coherently.
Migration gotchas
Converting between models is painful—decide up front. Document aliases, forwarding, and mobile app behavior.
Governance
Owners accountable for membership reviews quarterly; disable stale shared mailboxes after 90 days inactive per policy.
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