Send an email to firstname.lastname@example.org with the following message:
Please grant the 'email@example.com' user to "Full Access" permission for the following mailboxes:
Include the list of the Exchange mailbox names you would like to have delegate access to.
Article ID: 486
Last updated: 10 May, 2018
Also listed in
Riva On-Premise - CRM Sync -> Manage Riva On-Premise (Admin Guides) -> Email Systems -> Exchange (EWS) -> Hosted Exchange