I am having big troubles getting openpgp working with kmail.

I have a pair of keys which I use. In thunderbird I use enigmail and there I can sign and encrypt messages and it works. I have tried to send a signed and encrypted mail from thunderbird and open it with kmail, this works.

But when I read messages from mailinglists (kde-dev) with kmail all signatures fails. It also fails when I send a message to myself and try to sign it, encryption to self fails too..

I have followed the guide at http://kmail.kde.org/kmail-pgpmime-howto.html and I can't find anything obvious, except that my installed version of gnupg is 1.4.6.

Any ideas?

If gnupg itself is working (and that should be the same for TB and KMail), then if signature checks are failing it must mean that the content of the message is being changed at some point. Mailers sometimes "adjust" email content, for example by line-wrapping the content and encoding it as quoted-printable before transmission. If the receiving mail client doesn't decode the content before the signature check, the signature will not verify.

Is it possible that you have a setting somewhere in KMail that wraps/quotes messages, which is damaging the signature? Or are the messages from the mail-list you mention being mangled by the mail list handler for bulk distribution?

Are you using PGP-MIME in all cases, or inline PGP encoding? Does it make a difference if you try both methods?