The process of accepting a calendar sharing invitation by an external person is a bit different, but still very much straightforward in case you use Outlook for Office 365 or has an account. View calendar shared outside organization The calendar will appear in your Outlook under Shared Calendars: Simply open the sharing invitation that your colleague sent to you and click the Accept button at the top.
When a calendar is shared within the same organization, it can be added to Outlook with a single click. If you are using Outlook on the web (OWA) or, the detailed instructions are here: How to open a shared calendar in Outlook Online. This tutorial focuses on the desktop Outlook app installed locally on your computer.
