Moving from an old request of mine, I post here a script that I was suggested to put in /usr/share/kservice5/ServiceMenu directory, in Plasma5 environment.
In Plasma6 you have to put it in
/usr/share/kio/servicemenus/
the sendto.desktop file I attached below, and it will allow you immediately to mail a file by Thunderbird: by simply right-clicking the file, the voice "Mail by Thunderbird" will appear and you can send the file as attached one.
sendto.desktop.txt (319 Bytes)
Just get rid of .txt characters, and put the file sento.desktop in /usr/share/kio/servicemenus/.
It WORKS.