Kmail and smime

Hi,
i've a smime cert and try to use it with Kontakt/Kmail. It is imported
in Kleopatra and there is everything okay.
So i set it up in kmail to use this cert and when i try to write an
email, my email will be added with this smime.p7s and has the
signitar. So i send my mail, have to type my password for this cert
and then it will be sent. So i try it now to send it to me and then
it's a red sign, and it says: The signature is invalid: Incorrect
signature

So i try my smime with outlook in windows and in betterbird here on my
Manjaro KDE and with both apps it's working. Only with kmail there is
this problem.

Any idea where i could have a look in my settings? The smime setting
in kmail is filled with my smime-cert and this is "green", any other
option i could check maybe "default-domain" (i changed it now to our
real domain but this didn't work) or anything else?

Many thanks for some responses.

--=20
Mit freundlichen Gr=C3=BC=C3=9Fen
Sebastian G=C3=B6decke