Pre: You want to give person X access to the mailbox from persons Y.
Login as person Y and then follow the procedure below;
1. Start MS Outlook 2016.
2. Select “File”, “Info” and click on the “Account Settings” button.
3. Then select “Delegate Access”.
4. Then click “Add” to give another account acces to the Outlook account that is currently logged on.
5. In the “Add Users” screen, please search for the account name and click “Add”, followed by “OK”. The delegate screen will popup.
6. It is now possible to give the account access to several items.
7. Make sure Calendar, Tasks and Inbox got “Editor” access, if you want to enable “mail on behalf of” and add the mailbox as a second mailbox to the accounts Outlook.
8. Uncheck the box “Delegate receives copies of meeting-related messages sent to me.
9. Optional is to enable the checkbox “Delegate can see my private items” give the account access to calendar items created as a private appointment.
10. Click “OK”, and “OK”.
11. You are now finished.