Office 365 Calendar vs. Hosted Exchange vs. Exchange Online
Drift is currently compatible with Cloud-based Office 365 calendars & email.
You can confirm this yourself by visiting your Office 365 web login and logging-in with your calendar credentials.
You should see a calendar icon in the list that looks like this:

If you can see this calendar icon, and still have problems connecting your calendar to Drift, chat with us below so we can get help you out!
Note: Drift can only connect directly with Office 365. Exchange, Exchange Online and Hybrid Exchange calendars will not connect.
Permissions
It's possible to be an Office 365 user without having Calendar access. Check with your administrator to see if your team uses Hosted Exchange or Exchange Online for email and calendar and ensure that the role you are assigned in Office 365 includes calendar support.
You can view and manage your connection to Drift by visiting the Manage Connected Apps page of your Office 365 account