My User has Two Mailboxes?

This can occur under the following conditions:

• Scenario One: Migration fails to convert the source mailbox to a mailuser at the end of move request.
• Scenario Two: Admin provisions a cloud mailbox via directory sync, then mailbox enables the on-prem account.
• Scenario Three:Admin creates a new cloud only mailbox, then uses DirSync to soft-match a pre-existing on-prem mailbox to the account.
• Scenario Four: Admin migrates a mailbox to the cloud, then later mailbox enables the on-prem account

Details

Recovery Options

Scenario One

Essentially, you need to tear down the on-prem mailbox and convert it to a remote-mailbox recipient object while ensuring you have not lost any data between the two and have not lost any new incoming changes. Once that is complete you will have a correct configuration across the two premises that supports a properly functioning cloud mailbox.

Both mailboxes have a copy of the original content, so it is not necessary to back that content up specifically (although it is a great insurance policy to do so). You will need to copy out the content from the on-prem mailbox that the cloud mailbox does not have so you can restore it as the final step

There will be a period of time between exporting to PST, new changes being written to the mailbox, and the final disconnection. Any new email should be redirected away from the mailbox during this time so nothing is accidentally lost. The best option is to create a transport rule on-premises to redirect all messages destined for that mailbox and route them to the OnPrem-to-EOP send connector; this should result in delivery to the cloud mailbox. If this isn't possible, then at the very least email should be redirected to an alternative recipient where you can access it later.

1. Have end user logoff all of their sessions to the mailbox (all devices)
2. Stop the dirsync service (do not filter the user out of sync scope)
3. Copy all email addresses and legacyExchangeDN from the on-prem and cloud mailboxes
4. Redirect all mail destined to the on-prem mailbox through the OnPrem-To-EOP send connector.
5. Export the new content inside the on-prem mailbox to PST
6. Disable the on-premises mailbox
7. Mail enable the on-premises object as a remote mailbox
8. Add all email addresses back to the on-premisees object
   • Ensure targetAddress is included as an email addresses
   • Ensure both legacyExchangeDN values you copied in #3 are added as X:500 addresses
9. Enable dirsync and force a delta sync
10. Test connectivity: Exrca, Outlook, OWA
11. Remove the transport rule
12. Import content from the PST you created earlier

Scenario Two

You can follow the same steps that are listed in Scenario One. The on-premise mailbox is typically new and contains very little data (if any) in these circumstances, so the customer may opt to go straight for the mailbox-to-remotemailbox conversion (step 6 and 7).

Scenario Three

Typically, the desire will be to keep just the cloud mailbox while retaining all the content held between the two. To accomplish this, redirect new incoming email away from the cloud mailbox and store it somewhere else. The best option is to use a Criteria Based Transport Rule in EOP route it to the on-premises mailbox instead (all email sent to the cloud mailbox to be directed to the on-prem outbound connector (ability to do this may be limited across different environments). Once that is accomplished, mark the cloud mailbox as inactive, migrate the on-premises mailbox to EXO and then restore the data from the inactive to the migrated mailbox.

1. Have end user logoff all of their sessions to the mailbox (all devices)
2. Redirect new email to the on-premises mailbox, route the mail through the on-prem outbound connector.
3. Convert the cloud mailbox to an inactive mailbox.
4. Force a delta DirSync to provision a new cloud recipient
5. Migrate the mailbox, do not allow automatic completion of the move request
6. Remove the transport rule and complete the migration batch.
7. Apply an Exchange license to the user
8. Test connectivity: Exrca, Outlook, OWA
9. Perform a Mailbox restore request to copy the content of the inactive mailbox into the newly migrated mailbox.

You can follow the same steps that are listed in Scenario One.

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