SharePoint’s Cryptic Sharing Errors and Removing the Outlook Send Link Option

If you encounter an error when sharing a SharePoint file, you might see an error code like OSE204. What do these mainframe-like codes mean and why does SharePoint show them? Or more importantly, how did the sharing capability of a site change through administrator incompetence? And why is Microsoft removing the option to send a sharing link via Outlook (OWA)?