close 895823 thanks This was actually fixed with the removal of dovecot-common's postrm script with version 1:2.2.32-2 way back in 2017. However, that change never made it to the Debian 9 (stretch) branch, which I suspect is what led to this issue being encountered there.
In any case, as we are no longer updating the stretch branch, and haven't been in some time, there's nothing more we can or should do on this issue, and I am closing it. noah
