After you click the Test & Enable Mailbox button on a mailbox record in Dynamics 365 (online), you encounter the following alert:
"An internal Microsoft Dynamics 365 error occurred while synchronizing appointments, contacts, and tasks for the mailbox <Mailbox Name>. The owner of the associated email server profile <Email Server Profile Name> has been notified. The system will try again later.
Email Server Error Code: Crm.8004d24b.The user has not been assigned any License"