/usr/share/doc/syslog-ng-mod-smtp/changelog.Debian.gz is in syslog-ng-mod-smtp 3.5.6-2.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/syslog-ng-mod-smtp/../syslog-ng-core/changelog.Debian.gz