/usr/share/emacs/site-lisp/notmuch/ is in notmuch-emacs 0.21-3ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/emacs/site-lisp/notmuch/coolj.el
/usr/share/emacs/site-lisp/notmuch/notmuch-address.el
/usr/share/emacs/site-lisp/notmuch/notmuch-crypto.el
/usr/share/emacs/site-lisp/notmuch/notmuch-hello.el
/usr/share/emacs/site-lisp/notmuch/notmuch-jump.el
/usr/share/emacs/site-lisp/notmuch/notmuch-lib.el
/usr/share/emacs/site-lisp/notmuch/notmuch-maildir-fcc.el
/usr/share/emacs/site-lisp/notmuch/notmuch-message.el
/usr/share/emacs/site-lisp/notmuch/notmuch-mua.el
/usr/share/emacs/site-lisp/notmuch/notmuch-parser.el
/usr/share/emacs/site-lisp/notmuch/notmuch-print.el
/usr/share/emacs/site-lisp/notmuch/notmuch-query.el
/usr/share/emacs/site-lisp/notmuch/notmuch-show.el
/usr/share/emacs/site-lisp/notmuch/notmuch-tag.el
/usr/share/emacs/site-lisp/notmuch/notmuch-tree.el
/usr/share/emacs/site-lisp/notmuch/notmuch-version.el
/usr/share/emacs/site-lisp/notmuch/notmuch-wash.el
/usr/share/emacs/site-lisp/notmuch/notmuch.el