/usr/share/app-install/desktop/exo-utils:exo-mail-reader.desktop is in app-install-data 14.04.0.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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X-AppInstall-Package=exo-utils
X-AppInstall-Popcon=8779
X-AppInstall-Section=universe
Version=1.0
Type=Application
Exec=exo-open --launch MailReader %u
Icon=internet-mail
StartupNotify=true
Terminal=false
Categories=Network;X-XFCE;X-Xfce-Toplevel;
OnlyShowIn=XFCE;
X-XFCE-MimeType=x-scheme-handler/mailto;
Name=Mail Reader
Comment=Read your email
X-Ubuntu-Gettext-Domain=app-install-data
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