[tde-users] kmail as default for non-TDE apps

Sorry to use this forum that way, but I know someone here is bound to know the answer (I've been searching... without finding the correct answer). I use kmail as my email client. It's set up as default email client in TDE but other programs don't look there and start thunderbird. xdg-settings does not list anything for "default email client". Anyone know how to make non-tde programs (In this case Vivaldi) learn to use kmail? Thierry