On Debian Jessie (testing) the default ‘Send as Email Attachment’ context menu item uses KMail, and only KMail, even if you’ve configured your desktop to use Icedove (Thunderbird) as your default mail client.
So you can remove the broken ‘Send as Email Attachment’ from Dolphin by opening Dolphin then:
Settings -> Configure Dolphin… -> Services -> uncheck ‘Send as Email Attachment’
Then to create a replacement feature that uses Icedove edit:
~/.kde/share/kd4/share/icedove_attachment.desktop
And enter:
[Desktop Entry] Type=Service Actions=attachToEmail Encoding=UTF-8 ServiceTypes=KonqPopupMenu/Plugin,all/allfiles ExcludeServiceTypes=application/x-iso,kdedevice/*,inode/directory [Desktop Action attachToEmail] Exec=icedove -compose "attachment='$(echo %F | sed 's/\\ \\//,\\/\\//g')'" Name=Attach to Icedove Name[it]=Invia E-mail con Icedove Name[es]=Enviar adjunto con Icedove Name[de]=Als Anhang mit Icedove verschicken Name[pt]=Anexar ao Icedove E-mail Name[pt_BR]=Enviar arquivo(s) como anexo(s) Name[fr]=Envoyer avec Icedove Name[nl]=Voeg toe als bijlage aan Icedove Name[pl]=Wyślij jako załącznik Icedove Name[ru]=Отправить с помощью Icedove Name[cz]=Odeslat jako přílohu Icedove Icon=/usr/lib/icedove/chrome/icons/default/default16.png
And make sure your .desktop file is executable:
$ chmod +x ~/.kde/share/kd4/share/icedove_attachment.desktop