Manage your calendars in Microsoft Outlook to display all of your events from multiple sources, including Internet calendars. If you aren't able to view your appointments from another service ...

However, this offline calendar support only seems to apply to the new Outlook app. If you want to keep using classic Outlook, note that you’ll still have to be always online to manage your calendar.

Microsoft is investigating an ongoing outage preventing Outlook on the web users from accessing their Exchange Online mailboxes ... and intermittent plain text calendar invite emails with ...