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Exchange Online Troubleshooting: Problem in Hybrid Migration Where Mailbox still exist on-Premises

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Sometimes during Hybrid Migration you will practice an issue that is not actually an error, its a problem which you will face sometime in which when you create a batch of Users to migrate the Mailboxes or to hybrid the Mailboxes (NOTE: This issue might come with Cutover Migration also where Users Mailboxes completely Migrate to Cloud or Office 365). Some Mailboxes creates an issue that the Mailbox Migrated to Office 365 and Status on Office 365 will be COMPLETED, but still, the mailbox shows on-premises or status on Local Exchange Server will be "User Mailbox" Instead of "Remote Mailbox". Because the status "Remote Mailbox" means that your Mailbox has been migrated office 365 successfully and "User Mailbox" means that this mailbox exists on local exchange Server rather than remote.

Actually this issue could be due to some internet problems that if you are getting breaks in internet during Migration or User changes his password during Migration, or MRS proxy has some timeout issues.

Another Issue you will face due to this that when you will open Outlook of that specific person no matter what method you will adopt do it Automatically or Manually setup It will connect your Outlook to the Local exchange rather than Outlook.office.com or Exchange Online.

After so much research and did a lot of work to come to a very easy Solution which you can find below:

1. Disable the user's on-premises mailbox.

To do this, use one of the following methods:

  • Use the Exchange Management Console to disable the user's on-premises mailbox.
  • Use Exchange Management Shell to disable the user's on-premises mailbox. To do this, run the following Exchange Management Shell command: Disable-Mailbox <UserMailbox>

2. Convert the user's on-premises mailbox to a remote user mailbox.

To do this, run the following Exchange Management Shell cmdlet: 

Enable-RemoteMailbox  -Identity <UserName> -RemoteRoutingAddress <UserName@domain.mail.onmicrosoft.com>