/usr/lib/tmpfiles.d/courier-imap.conf is in courier-imap 4.17.2+0.76.3-5+deb9u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | #Type Path Mode UID GID Age Argument
d /run/courier 0775 root courier - -
|