You may receive the below error message when adding Shared Calendars in Outlook for Mac. This occurs even when the permissions are set in the webmail:
"Outlook cannot open the folder."
You do not have permission to open this folder. Contact '<firstname.lastname@example.org>' for permission.
This article provides step-by-step instructions on how to enable Shared Calendars in Outlook for Mac.
Configure your Exchange Web Services (EWS) account in Outlook for Mac.
Configure the Calendar sharing feature via webmail.
Ensure that the necessary Calendar folders are synced.
Go to Tools > Accounts > Advanced.
Go to the Server tab > Enable the Sync shared mailbox option.
Go to the Delegates tab > Open these additional mailboxes and add the desired user using the + sign.
Restart Mac Outlook.
Shared Calendars are displayed in the Calendar tab.