1. Go to webmail.htop.org
2. Log in with an account with admin privileges
3. Open the Admin App
4. Under Admin Center, click Exchange Admin Center
5. Click Recipients
6. Search for the mailbox you need to give permission to by clicking the hour glassĀ 
7. Double Click on the mailbox you want to edit
8. Click mailbox delegation
9. Under Full Access, add the user