Hey Anthony, Jared, and Eric, I really can't thank you enough for all the insights and direct assistance you've recently provided in relation to my difficulties with Thunderbird and Cloudflare. My interest in Cloudflare is two-fold. First, perhaps from NMCSLUG meetings, Anthony may remember that for some time I've had this notion that maybe if I got set up to use Cloudflare I would be to some extent bypassing Comcast's undesirable potential for abusing it's position as a gatekeeper. Second, through his help with troubleshooting the quirky behavior of my instances of Thunderbird and IMAP servers under Kubuntu 18.04 (multiple, thanks to Jared), Anthony posited that symptoms indicate problems with local networking. Hence, he suggested that I should reset DNS servers to Google or Cloudflare and try again, presumably to confirm and narrow things down. Whereupon I remembered old roadblocks and confusion I'd encountered some months back trying to get my computer to talk to Cloudflare servers. (No problem with Win 10 VMs, but no recommendations seemed to apply properly to my particular Linux circumstances.) So after whining to but not hearing back from Anthony, on whom I did not wish to overly presume, I put to NMGLUG my recent query for assistance with Cloudflare. Shortly thereafter Anthony chimed in again and very generously and quickly substantially reproduced, validated and overcame difficulties and concerns I'd had previously. He documented his journey and solution for me in a clear and comprehensive how-two (ultimately modify /etc/systemd/resolved.conf and restart resolved). Also, simultaneously, Eric responded with great information about Netplan, something I'd never even heard of (new to Kubuntu as of 18.04; configure the entry in a yaml file you'll find in /etc/netplan; a link to Netplan examples).
From my readings, Netplan seems to imply a very elegant solution approach that appears to me to have potentially broader applicability, considering both of the interests I mentioned above.
I've tried to poke around and grok everything; and, I intend to give it all further study. But obviously I'm thinking it can't hurt to submit this summary for further discussion and suggestions from any interested participants and observers before I start monkeying around again. I'll be working on it all as time and opportunity presents. But at the moment, I'm not yet particularly confident that I possess sufficient comprehension of the issues so that I won't screw up something important. Clearly, backups of involved files are in order, etc. It's all still pretty scary to me. Thank you for patiently holding my hand and not telling me to go RTFMP. Also, I thought I might ask about Avahi. Might it also be involved; should it be taken into consideration? Tom