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How to Migrate a Shared Mailbox to Exchange Online

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Written Bysysc.org Editorial Team
Published OnNovember 4, 2026
Reading Time3 Min Read
Quick Answer. Shared mailboxes move as regular mailboxes first. Convert the mailbox to shared after the move. Shared mailboxes store 50 GB without a license. Plan 2 licenses raise the limit to 100 GB. Unlicensed mailboxes can disconnect within 30 days.

What Rules Apply to a Shared Mailbox in Exchange Online?

Microsoft lists 50 GB as the limit for a shared mailbox without a license. An Exchange Online Plan 2 license raises the limit to 100 GB.

PointShared mailbox rule
LicenseNot needed up to 50 GB
Size above 50 GBNeeds Exchange Online Plan 2 or a Plan 1 with the archiving add on
AccessUsers who open it need an Exchange Online license
Sign inNot used, you open it through delegation

How do You Migrate It in a Hybrid Setup?

Method #1: Move, Then Convert (Free)

Who it suits. Admins with an Exchange hybrid deployment. Extra application. Exchange Management Shell and Exchange Online PowerShell.

  1. Move the mailbox to Exchange Online as a regular mailbox and assign a temporary license.
  2. Convert the on premises remote mailbox with the command below.
  3. Convert the cloud mailbox to shared in Exchange Online PowerShell.
  4. Remove the temporary license if the mailbox stays under 50 GB.
Set-RemoteMailbox -Identity <mailbox ID> -Type Shared
Set-Mailbox -Identity <mailbox ID> -Type Shared

Microsoft explains why both steps matter. Synchronization flows from on premises to the cloud, so a type mismatch can revert the shared mailbox to a regular mailbox. A regular mailbox with no license and no hold can disconnect, and you can lose the content if you do not fix it within 30 days.

What should You Check Before and After?

  • Check the mailbox size against the 50 GB limit.
  • Assign the temporary license before the move ends.
  • Confirm the type reads SharedMailbox on both sides.
  • Test Full Access and Send As permissions with one delegate.
  • Remove the license only when the size permits it.

Our Exchange mailbox size limits guide lists the limits by plan, and the Exchange Online migration checklist lists licenses and DNS.

What if You do Not Use Hybrid?

Cutover and staged migrations move mailboxes in batches, as our cutover vs staged vs hybrid guide explains. Plan the same sequence after the batch ends. Check the mailbox type in Exchange Online and use Set-Mailbox with the Shared type when it shows as a regular mailbox.

Heads Up. Microsoft documents the full sequence for hybrid setups. Test the steps on one non critical mailbox before a batch.

Frequently Asked Questions

Does a Shared Mailbox Need a License?

No, not up to 50 GB. Microsoft lists 50 GB without a license and 100 GB with a Plan 2 license.

How do You Migrate a Shared Mailbox in Hybrid?

Move it as a regular mailbox, convert the remote mailbox to shared and convert the cloud mailbox to shared.

Which Command Converts the Cloud Mailbox?

Use Set-Mailbox with the Identity and the Type parameter set to Shared in Exchange Online PowerShell.

Why can a Shared Mailbox Revert to a Regular One?

Microsoft states that a type mismatch with the on premises remote mailbox can cause it.

How Long do You have to Fix a Disconnected Mailbox?

Microsoft states that you must finish within 30 days or you can lose the content.

When do You Remove the Temporary License?

Remove it after the mailbox is shared on both sides and stays under 50 GB.

Do Delegates Need Licenses?

Microsoft states that users who open a shared mailbox need an Exchange Online license.

Author's Verdict

Move first, convert second and remove the license last.

Check the type on both sides, because a mismatch causes most disconnect problems.

Key Takeaways

  • Shared mailboxes move as regular mailboxes.
  • Convert on premises and in the cloud.
  • Retain the license when the mailbox passes 50 GB.

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