Kirby email function with umlaute

When email function is sending a message with some special characters (umlaute) ü,ö,ä, they are showing as weird symbols…

I have tried several things like

header('Content-Type: text/html; charset=utf-8');

but this does not solve.

Anyone has some solution for me?

Cheers,

Carsten

Solved it with adding utf8_decode() on my string which is added in the email body.