One more piece of the puzzle: the explanatory comment text in
/etc/dovecot/conf.d/auth-system.conf.ext:
# LDA and LMTP needs to look up users only from the userdb. This of course
# doesn't work with static userdb because there is no list of users.
# Normally static userdb handles this by doing a passdb lookup. This works
# with most passdbs, with PAM being the most notable exception. If you do
# the user verification another way, you can add allow_all_users=yes to
# the args in which case the passdb lookup is skipped.
This explains why the static userdb prevented the system user from
being recognized, since it was in PAM not /etc/passwd.
--
Randall Gellens
Opinions are personal; facts are suspect; I speak for myself only
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The first ninety percent of the task takes ninety percent of
the time, and the last ten percent takes the other ninety percent.
