Bingo! Your question wasn't silly at all. libsasl2-modules wasn't
installed and installing it cured the problem. post now works
beautifully. Many thanks, and apologies for this lacuna and the time
wasted.
As to how it came about, I can see that the Debian libsasl2-2 package
"recommends" libsasl2-modules, but in default I use
'Apt::Install-Recommends "false"' on the grounds that in general
"true" drags down just too much unwanted dead wood. I guess I will
have to be more careful in future.
Many thanks anyway.
Tony
--
Tony Stoneley
Preferred email address ajms(_at_)cam(_dot_)ac(_dot_)uk
...not withstanding anything any ISP may force into my "From:" field
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Ken Hornstein wrote on Thu, 03 Feb 2022 14:29:30 -0500
I have one silly question: did you install the libsasl2-modules package?
That's the package that actually contains the sasl mechanism for PLAIN
(along with others). There should be something like "libplain.so" in
a directory close to /usr/lib/x86_64-linux-gnu/sasl2 depending on your
architecture.