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How to convert a user mailbox to a shared mailbox

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How to convert a user mailbox to a shared mailbox

How to convert a user mailbox to a shared mailbox in Exchange Online, when it's the right leaver move, the 50 GB and hold rules, and removing the licence.

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Do shared mailboxes need a licence?

Not up to 50 GB and without an archive, litigation hold, or retention hold. A shared mailbox over 50 GB, or one that needs an archive or a hold, needs an Exchange Online Plan 2 licence (or an Exchange Online Plan 1 plus…

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02

Can I remove the licence straight after converting to shared?

Wait until the conversion shows complete in the admin center and the mailbox size is under 50 GB with no holds. Removing the licence while the mailbox is still a user mailbox triggers the 30-day soft-delete path, not co…

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Should I convert a leaver's mailbox to shared or just keep it licensed?

Convert when someone else needs ongoing access to the mail (a role handover), the mailbox is under 50 GB, and there is no legal hold. Keep it licensed as an inactive or held mailbox when retention or legal requirements…

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Step 1: Check size and holds

If a hold applies and legal wants it kept, stop here and keep the licence; conversion still works but changes nothing about licensing.

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Step 2: Block sign-in and clear the password

If this is a leaver, block sign-in in the Microsoft 365 admin center (or Entra) and revoke sessions before converting. A shared mailbox has a disabled account by design, but a converted mailbox keeps whatever sign-in st…

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Step 3: Convert

Exchange admin center: Recipients → Mailboxes → the mailbox → Others → Convert to shared mailbox. Or:

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Step 4: Grant access

Full Access with auto-mapping makes the mailbox appear in the successor's Outlook automatically. Use Send on Behalf (Set-Mailbox -GrantSendOnBehalfTo) instead of Send As if replies should visibly come from the successor.

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