[Quick Fix] How To Solve Mailbox Exists On-premise And Office 365?

The strategies in this post help you on how to solve mailbox exists on-premise and office 365.

Here is the sample user who has a mailbox in on-premises.

The same user also has a mailbox in cloud.

I have a couple of options to resolve the issue. Let’s discuss each options.

Fix 1: Remove Exchange Online License

In the Microsoft 365 admin center, go to the Users > Active users page.
Search the affected user account.
Select Licenses and Apps.
Expand the Licenses section, clear the boxes for the licenses that you want to unassign, then select Save changes.
After removed the license, the account will appear as a mail user in cloud.

Now, the mailbox in on-premises needs to be migrated to Exchange online and add the necessary license again.
Once the mailbox appears ok in Microsoft 365, perform the mailbox restore request to move mailbox contents from the soft-deleted mailbox to the active mailbox.

New-MailboxRestoreRequest -SourceMailbox “Softmailbox@techieberry.com” -TargetMailbox “Activemailbox@techieberry.com” -AllowLegacyDNMismatch

As you are aware, exchange online mailbox is associated to Azure Active Directory account.
Connect to Azure PowerShell. To initiate a connection, use Connect-Msolservice.
Remove the user account using the Remove-Msoluser command. For example, Remove-MsolUser -UserPrincipalName test248@techieberry.com -Force
After the account is removed, the mailbox in cloud will be moved to soft-deleted state. It will not appear in the active users list.

After sync is complete, the on-premises account will sync to Azure Active Directory as a mail user.

Now, you need to migrate the migrate the on-premises mailbox to Exchange Online and assign the appropriate license.
Once it is done, perform the mailbox restore request to move mailbox contents data from the soft-deleted mailbox to the active mailbox.

For more information about mailbox exists on-premises and office 365, check the Microsoft website.

Want to improve your Exchange Online experience for better productivity? Check out the tips and tricks mentioned here.

Now I’d like to hear from you:

Which options from today’s post are you going to try first? Or maybe you have a question about something that I covered.

Either way, let me know by leaving a comment below right now.