thanks for responding, I will try this out at home. Microsoft Outlook for Mac 2011 does not have this functionality, although the Windows version has for years.
I figured other users might have this type of problem as well but for all the downvotes...I guess not.
This minor feature was enough to drive me away from Mac Mail, and Outlook for Mac, over to Outlook on a Windows Virtual Machine.
Having a high-res 27" monitor is a blessing in many ways, but a literal headache in others, particularly late night.
I agree this is not very discoverable compared to the usual Zoom In / Zoom Out menu items. Mail suffers from its age in many ways.