A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Thanks for that link. I wasn't aware that behavior could be modified.
Aside from that, stealth mode is an important security feature and I would not turn that off just to work-around a (temporary) bug in Outlook/Excel. Turning that feature off allows for easy reconnaissance of your Windows-based infrastructure.
Adding an outbound rule on the clients does not increase my exposure so I'm sticking to that until this issue is solved.