I would like to try Maui..

[Gorreh]

hey? are you there?
I put Maui to my "testing" laptop, so far so good

ok, below solution to add TB in Dolphin content menu: you need modified ~/.local/share/kservices5/ServiceMenus  

[Desktop Entry]
Type=Service
Actions=sendto
Encoding=UTF-8
MimeType=application/octet-stream
X-KDE-ServiceTypes=KonqPopupMenu/Plugin

[Desktop Action sendto]
Name=Send e-mail using Thunderbird.
Exec=thunderbird -compose "attachment='$(echo %F | sed 's/\\ \\//,\\/\\//g')'"
Icon=thunderbird 

sources http://www.grim.se/guide/sendto

I coudn't find solution how to setup KDE to work properly with autostart&Thunderbird 
regards
gorreh