Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Not quite sure what you're describing. Are messages missing?
Have you possibly closed the Navigation pane on the left that displays your Inbox and other folders? If so, select View menu --> Navigation Pane to restore it.
If this doesn't answer your question then please post back with more details about what you're seeing and what you expect to see.
Hope this helps!