/usr/share/xfce4/helpers/opera-mailer.desktop is in libexo-helpers 0.10.2-3ubuntu1.
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 | [Desktop Entry]
Version=1.0
Icon=opera
Type=X-XFCE-Helper
Name=Opera Mail
Name[bg]=Опера Поща
Name[fi]=Operan sähköposti
StartupNotify=false
X-XFCE-Binaries=opera;
X-XFCE-Category=MailReader
X-XFCE-Commands=%B;
X-XFCE-CommandsWithParameter=%B -remote "openURL(mailto:%s)";%B "mailto:%s";
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