Why am I not receiving new email alerts and calendar invites with Android 9 (Pie)?

If you are using Android 9 (Android Pie), a feature in the build may be restricting Outlook's background usage. In order to reenable Outlook alerts:

1. Close and relaunch Outlook.
2. Click VIEW on the notification regarding restricted background usage at the bottom of the screen.
3. Click View Settings.
4. Go to Manage Battery Usage.
5. Find Outlook's settings, then go to Battery Usage or Use Details.
6. If Background Restriction or Allow Background Activity is restricted, click on it to disable the restriction.