If – for some reason – a mailbox migration to Exchange Online fails, the retry procedure may be a bit dodgy, behold…
Let’s imagine having a user named Francis with an on-premise mailbox. This user is member of a specific department that requires delegated mailbox access across all members, so we create a single batch with all users of this department. Most members migrate properly at first try, but several users, including Francis, fail. The summary shows:
The per-user error is:
“Error: MigrationRecipientNotFoundException: A recipient wasn’t found for “firstname.lastname@example.org” on the target. Create a recipient of the appropriate type for this migration on the target and try again.”
Turns out, the user wasn’t synced all that well to Azure AD, apparently this happens from time to time. After triggering another sync with the AD Sync tool, the user now appears in Azure AD with all its properly set attributes. So let’s retry the mailbox migration:
Ok, well this is awkward… Nothing happened? Looking at the mailboxes summary, refreshing at least 3 times Francis still has no online mailbox. After much investigation, I came to the following conclusion:
It turns out you cannot successfully retry a mailbox migration if there is a failed migration in any of the batches. It will appear as ‘Completed’, but in fact the migration will not do anything.
So, we remove the failed migration items from the mailbox migration batch and put them in a new batch. The result?
Office 365 works in mysterious ways 🙂