/usr/ is in squirrelmail-sent-confirmation 1.6-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/
/usr/share/squirrelmail/
/usr/share/squirrelmail/plugins/
/usr/share/squirrelmail/plugins/sent_confirmation/
/usr/share/squirrelmail/plugins/sent_confirmation/setup.php
/usr/share/squirrelmail/plugins/sent_confirmation/functions.php
/usr/share/squirrelmail/plugins/sent_confirmation/index.php
/usr/share/squirrelmail/plugins/sent_confirmation/address_book_import.php
/usr/share/squirrelmail/plugins/sent_confirmation/options.php
/usr/share/squirrelmail/plugins/sent_confirmation/locale/
/usr/share/squirrelmail/plugins/sent_confirmation/locale/sent_confirmation.pot
/usr/share/doc/
/usr/share/doc/squirrelmail-sent-confirmation/
/usr/share/doc/squirrelmail-sent-confirmation/copyright
/usr/share/doc/squirrelmail-sent-confirmation/README.gz
/usr/share/doc/squirrelmail-sent-confirmation/changelog.Debian.gz
/usr/share/squirrelmail/plugins/sent_confirmation/config.php