I may have led you astray about too many emails being the problem.
Actually, after stumbling upon the configuration in the network settings menu that resulted in a successful test and having emails successfully sent upon motion detection, the camera simply stopped sending emails.
When I noticed the emails had stopped, I performed the internal camera test again and it failed! Nothing had changed in the camera settings.
So, what can you think of that might have changed either on the desktop PC or the Outlook server that caused a working camera email delivery system to fail the internal test?