Early in 2018, around the time when I upgraded my system to Windows 10, the Stunnel and Blat files that had worked fine with my Vista PC would not work with the new PC.  However, the "bug" turned out to be unrelated to the change in operating systems, but rather an "upgrade" to Gmail:  Coincidentally, about that time, Gmail evidently decided to stop accepting e-mails from apps deemed "a less secure app", including Stunnel-Blat, with Blat then displaying messages:

Only a failure message sent to my "backup e-mail address" led me to explore this as a possible cause for what I had thought was, but turned out not to be, a Stunnel-Blat problem.  Gmail has an option to suppress this heightened security feature, and when I activated this option, my Stunnel-Blat tools immediately began to function as intended.

While I was at first able to enable Gmail to "Allow access from "less secure accounts," I have been unable to get through Gmail options consistently to turn this on and off and share this info with others.  (I would welcome instructions that work consistently.)

I would also welcome guidance on how to include Stunnel-Blat as a specific alllowed app, without having to enable Gmail to enable all "less secure apps"