Thanks all for the good discussion.
Ok. To summarize, change the Output Options back to mobi: old. Leave Behavior output set to mobi. All should be good.
My convoluted workflow is to have Amazon send my purchased book to my PC (to the folder of my choice). I then import the new book into Calibre and then send it to my PW2014.
Where I encountered email issues was trying to send some old books in my library (that weren't in the partial collection Amazon had from my old K3) after initially setting up Calibre. I'm not sure what happened there, but I got around that issue by sideloading the ebooks in question. The old Calibre installation had no problem emailing ebooks to my K3. [shrug]
Next to see how it plays out down the road with my current revised settings.
(I don't recall my Calibre settings from the old installation).