Debian 9.2 Exim4 "vs." Eximconfig
Ah, drats, found (and thus far partially) corrected one other glitch. /etc/exim4/eximconfig/bin/spfd doesn't play very well - at least as provided with the spfd on Debian. I checked, found emails getting temporary rejections due to the Eximconfig configured to use spfd, but not managing to talk to it. Turns out there's syntax changes on invoking the Debian provided spfd (at least the one I've got installed) ... and compared to whatever I had before with Debian 8.9. And rather oddly also, for /etc/exim4/eximconfig/bin/spfd where does it have its configuration on how it invokes the operating system provided spfd? In /etc/exim4/eximconfig/bin/spfd itself! It also has some odd funkiness and really ought do with a more proper rewrite (e.g. it's status functionality is seriously flawed - thus it fails to detect that spfd is already running, fails to stop it, starts multiple instances of it). Anyway, have it "working" at the moment - at least up and functional. Need to make more adjustments to /etc/exim4/eximconfig/bin/spfd so it's more operationally functional ... notably so it's status and stop arguments work, and it's start argument will detect when spfd is actually already running.
I get the sneaking suspicion I may end up replacing much or all of Eximconfig with something much more maintainable ... and reasonably current ... though it may still serve as reference on general approach, but seems hazardously outdated as to actual configuration, etc.