Exchange Online–Clearing for good previous mailbox information

This update will be very interesting for migration context to Exchange Online – may be other situation too but can’t see it right now.

Microsoft is introducing a new parameter to the Set-User command to permanently remove previous Exchange Online details.

Imagine the following scenario:

  • User have Exchange On Premises mailbox
  • You have Azure AD Connect in place and synching
  • You prepare to migrate the mailbox and assign an ExO license to the user
  • Unfortunately there was an issue which blocked the Exchange On Prem GUID to be synchronized and so you ended with 2 mailboxes for the user: one On-Prem and one Online

Removing the online mailbox has been always tricky in this situation because you have a 30 days retention period; meaning even when you remove the ExO license, the next time you will re assign the license ExO will automatically reassociate the ‘wrong’ mailbox.

There was no other way than deleting the online user account, but this also impacts other Office 365 workloads.

With this update, you will be able to get rid for good of the ‘incorrect’ Exchange Online mailbox

Set-User <email address> –PermanentlyClearPreviousMailboxInfo

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