/usr/share/doc/claws-mail-tools/RELEASE_NOTES is in claws-mail-tools 3.9.3-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/claws-mail-tools/../claws-mail/RELEASE_NOTES
/usr/share/doc/claws-mail-tools/../claws-mail/RELEASE_NOTES