Office 365: Fatal error RecipientNotFoundPermanentException has occurred

In Office 365 administrators may experience almost immediate failures of migrations to Office 365.  The error is typically in the following format:


Error: Cannot find a recipient that has mailbox GUID 'MAILBOX-GUID'.


The migration log shows the following information at the end of the log regarding the failure exception”":


9/11/2017 9:13:58 PM [DM5PR04MB0988] Fatal error RecipientNotFoundPermanentException has occurred.


The error itself is quite misleading at casual glance.  The recipient can be located on premises as well as in Office 365.  If the recipient can easily be located – why is the migration failing with this error?


Further review of the migration log shows entries similar to the following:


9/11/2017 9:13:54 PM [DM5PR04MB0988] Content from the Shard mailbox (Mailbox Guid: MAILBOX-GUID, Database Guid: DATABSE-GUID) will be merged into the target mailbox.


The GUID listed in MAILBOX-GUID for the SHARD mailbox matches the MAILBOX-GUID in the error.  We cannot locate the SHARD mailbox.  What is a SHARD mailbox?


In Office 365 on premises mailbox are represented by mail user objects.  It is possible that you have migrated mailboxes to Office 365 and these users are collaborating with users that have not yet been migrated.  The services they are collaborating on may store data within the Exchange Online mailbox.  A user that has not been migrated – being a mail user object – typically does not have a mailbox to store data in.  In order to facilitate this collaboration we create a special mailbox known as the SHARD mailbox.  The administrator can view SHARD mailboxes using the get-MailboxLocations commandlet.  IT IS PEFECTLY NORMAL FOR A MAIL USER NOT YET MIGRATED TO HAVE A SINGLE COMPONENTSHARED MAILBOX TO FACILITATE COLLABORATION.


Get-MailboxLocations –identity ALIAS


RunspaceId : d075c233-05d4-4b41-9c2d-3fbc930d593f
MailboxGuid : GUID
DatabaseLocation : NAMPR06DG007-db108
MailboxLocationType : ComponentShared
OwnerId : NAME
TenantGuid : GUID
MailboxMoveBatchName :
MailboxMoveStatus : None
MailboxMoveFlags : None
RawExternalEmailAddress :
MigrationDryRun : False
OptInUser : False
IsMigratedConsumerMailbox : False
IsPremiumConsumerMailbox : False
PrimaryMailboxSource : None
MailboxProvisioningConstraint :
SiloName :
Identity : GUID\GUID
IsValid : True
ObjectState : New


When the administrator provisions a migration to Office 365 for a user with a SHARD mailbox the migration process attempts to locate the mailbox in the defined database.  As a post migration activity we will merge the contents of the SHARD mailbox into the primary mailbox that was migrated.  The SHARD mailbox is then decommissioned as it is no longer necessary.  The error we are receiving in this case  is the result of the migration process being unable to locate the SHARD mailbox.


In order to correct this condition administrators should open a support ticket and work with product support services.


*Updated 11/20/2017


An update to this blog post contained a script that could be used to identity duplicate shard mailboxes.  The migration process now handles this condition – the post was reverted to the original information which may require product support services.