Mail sent from an Office 365 user to a synced, but not switched Shared mailbox, is delivered to the corresponding 365 Shared mailbox and not to the Source mailbox as expected.
When using the Migration Manager for Active Directory (Office 365) to Migrate that account, the following error is received in the QsDirectoryMigrationAgent.log:
The operation on mailbox "<mailbox>" failed because it's out of the current user's write scope. The action 'Set-Mailbox', 'EmailAddresses', can't be performed on the object '<mailbox>' because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.
Shared mailboxes under 50GB can be created on Office 365 without using an Exchange Online license. However, if it does not have an appropriate license, and already exists as a Shared Mailbox in Office 365, Migration Manager for Active Directory (Office 365) cannot set the Redirector address appropriately. This attribute is the ForwardingSMTPAddress in Office 365.
Assign an Exchange Online license to the Shared Mailbox.
Migrate the account using Migration Manager for Active Directory (Office 365) to set the Redirector address on the Office 365 mailbox.
