Office 365 Mac Outlook: Cannot add delegate mail account.

bsweetman PeterRising It looks like your user is using "New Outlook", which doesn't appear to have the Advanced settings, or even allow Delegate Accounts.

The only way I've found to view Delegate Accounts is to turn off "New Outlook" using the switch in the top right corner (see attached) - Outlook will restart and you will regain the Advanced setting under Accounts.

It appears that even after adding the Delegate Account under the "old Outlook", switching back to "New Outlook" hides the account & related settings, so you'll need to avoid it for the time being.