/usr/share/kde4/services/plasma-applet-mail_plasmoid.desktop is in plasma-widget-mail 0.3.1-0ubuntu7.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | [Desktop Entry]
Name=mail_plasmoid
Comment=Checks your mailbox for new messages
Type=Service
ServiceTypes=Plasma/Applet
X-KDE-Library=plasma_applet_mail_plasmoid
X-KDE-PluginInfo-Author=Sebastian Wankerl
X-KDE-PluginInfo-Email=far_away@online.de
X-KDE-PluginInfo-Name=plasma_applet_mail_plasmoid
X-KDE-PluginInfo-Version=0.2
X-KDE-PluginInfo-Website=http://plasma.kde.org/
X-KDE-PluginInfo-Category=Utilities
X-KDE-PluginInfo-Depends=
X-KDE-PluginInfo-License=GPL
X-KDE-PluginInfo-EnabledByDefault=true
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