I recently had the case that after a tenant-to-tenant Azure Migration, one of the users wanted some days later to recover their Mail Calendar Meetings to the new tenant with the new user.
The Only Problem to that was that the old user was already deleted in Azure AD in the old tenant and I was not able to Recover it via the GUI or PowerShell.
Luckily for me the solution was pretty easy 🙂 Just pay attention that you can only do it within the time the deleted mailbox is being kept as soft-deleted and not permanently deleted
First you need to create a new User in AAD and Assign the user a valid license with Exchange Online mailbox included. In my example I used a test business premium license I had in the tenant
Now you are pretty much ready for the restore of the Mailbox.
Open PowerShell and install the ExchangeOnlineManagement Module:
Next Create a new Mailbox Restore Request:
New-MailboxRestoreRequest -SourceMailbox <Soft-deleted Exchange Online Mailbox> -TargetMailbox <The Mailbox of the new User you created, where you want to restore> -AllowLegacyDNMismatch
Depending on the mailbox size it could take a while. You can use the Get-MailboxRestoreRequest CMDLet to monitor the Progress
