Originally from this Spanish blog
Kubuntu lets you right-click on a file and gives you the option to “email file”, but it will try to send it with the KDE email program, kmail. I use Thunderbird. Let’s fix that action:
Edit the file:
/usr/share/kubuntu-default-settings/kde-profile/default/share/apps/konqueror/servicemenus/email.desktop
to read:
[Desktop Entry]
Actions=Email
Encoding=UTF-8
ServiceTypes=allfiles[Desktop Action Email]
Name=Email File
Exec=thunderbird -compose `echo attachment=\‘file://%F\’ | sed ‘s/ \//,file:\/\/\//g’`
Icon=thunderbird