/usr/lib/x86_64-linux-gnu/ is in libkf5mailtransport-dev 15.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/x86_64-linux-gnu/cmake/
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/KF5MailTransportTargets.cmake
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/KF5MailTransportConfig.cmake
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/FindSasl2.cmake
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/KF5MailTransportConfigVersion.cmake
/usr/lib/x86_64-linux-gnu/cmake/KF5MailTransport/KF5MailTransportTargets-debian.cmake
/usr/lib/x86_64-linux-gnu/qt5/
/usr/lib/x86_64-linux-gnu/qt5/mkspecs/
/usr/lib/x86_64-linux-gnu/qt5/mkspecs/modules/
/usr/lib/x86_64-linux-gnu/qt5/mkspecs/modules/qt_KMailTransport.pri
/usr/lib/x86_64-linux-gnu/libKF5MailTransport.so