/usr/lib/libcourierauthcommon.so.0 is in courier-authlib 0.66.4-9.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libcourierauthcommon.so.0.0.0
/usr/lib/libcourierauthcommon.so.0.0.0