ODM Hybrid mailbox migration error, "This user's on-premises mailbox hasn't been migrated to ‎Exchange Online‎" (4350373)

When using the On Demand Migration (ODM) Hybrid module to migrate accounts from the source local Active Directory to the target Active Directory, you may encounter the following error:

This user's on-premises mailbox hasn't been migrated to ‎Exchange Online‎. The ‎Exchange Online‎ mailbox will be available after migration is completed.

If you have users in the source local Active Directory environment that previously had on-premise Exchange accounts in the source, then those users likely have the following attributes populated in the source Active Directory:

msexchmailboxguid
msexchrecipientdisplaytype
MsExchRecipientTypeDetails

Currently, the ODM Hybrid module will sync these attribute values to the target local Active Directory, which in turn will sync these attribute values to Office 365 via Azure AD Connect. However, syncing the "msexchmailboxguid" attribute value in particular will prevent a target Office 365 mailbox from being created by the ODM mail migration.

WORKAROUND

In order to workaround this issue, you will likely need to clear the "msexchmailboxguid" attribute value from target user objects that were synced by the ODM Hybrid module, that don't have on-premise mailboxes. You may wish to leverage PowerShell, outside of ODM, to clear these attributes.

STATUS

A product defect has been logged for this issue, ODM-1346, and is waiting for a fix in a future version of On Demand Migration.