/usr/share/man/man5/defaulthost.5.gz is in nullmailer 1:1.13-1.2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man5/../man1/nullmailer-inject.1.gz
/usr/share/man/man5/../man1/nullmailer-inject.1.gz