You have a hybrid deployment of on-premises Exchange Server and Exchange Online in Office 365 in which primary mailboxes are located in the on-premises environment and archive mailboxes are located in Exchange Online. When you try to move only a primary mailbox from the on-premises environment to Exchange Online by using the Exchange admin center in Office 365, you receive the following error message.
Error: MigrationPermanentException: You must specify the PrimaryOnly parameter
The Exchange admin center doesn't have the option to move only a primary mailbox. To do this, you must use the New-MoveRequest cmdlet.
To move only a primary mailbox, follow these steps:
Microsoft Exchange Online, Exchange Server 2016 Enterprise Edition, Exchange Server 2016 Standard Edition, Microsoft Exchange Server 2013 Enterprise, Microsoft Exchange Server 2013 Standard, Microsoft Exchange Server 2010 Enterprise, Microsoft Exchange Server 2010 Standard