To verify that Reminders are enabled, go to the Apple Menu and navigate to System Preferences. Once in System Preferences, click on Internet Accounts. In the left-hand pane, select the account you wish to configure. To enable/disable, check/uncheck the check box next to Reminders.

1. Open the Reminders
2. Click on the Reminders menu, then select ...
3. Select the Exchange
4. Enter your account credentials for the Office 365 environment, then select Continue.
5. Amongst the list of apps to sync, select Reminders, then click Done.
6. You will now see that an Exchange/Reminders account has been created. Click the red button to exit this screen (see arrow).
7. In the Reminder list you will now see the Exchange account that was just added.
   • Note: The process to move reminders will require copying and pasting selected tasks from the On My Mac group to the Exchange 
8. On the left hand side, under On My Mac, select the list meant for exporting. The selected list will be highlighted in maroon.
   • Note: This step will need to be repeated for each additional list of reminders that need to be transferred.
9. To transfer the entire list of tasks, select a task from the list, go to the Edit menu, then choose Select All.
10. Return to the Edit menu, then select Copy.
11. Under the Exchange group, select Tasks (see arrow). The selected task list will be highlight in maroon. Return to the Edit menu, then select Paste.
12. Your tasks are now available in the Office 365 web interface.