If you are positive! that no WU happened, or, that you did not pick up malware where both could take effect after a reboot, or in the interim a change in your router, modem, or ISP, or GMAIL servers ...these are the things that seem likely to narrow it down to the cause.
Well, I can definitely say that I am dumb as a post (is that the right phrase?). I went through all the stuff in #575, but didn't think of the obvious -- an update to a program being the culprit. Apparently Internet Download manager version 6.35 Build 9 broke things, so build ten simply said "[f]ixed a critical bug" in the change log. After updating to said build, things are once again working. Honestly, when will I learn to not overlook the simplest of solutions?
I'm a creature of habit, so thanks to endeavor a great deal for enabling me to continue to use Windows Mail until I can no longer do so. I really should switch to something else one of these days, but there's nothing that beats the speed and simplicity of Winmail without being a bigger resource hog.
- Windows 10 Version 1607 (OS Build 14393)