Version: (using KDE 4.4.2) OS: Linux Installed from: Ubuntu Packages The certificate of the largest german email provider GMX is no more accepted by konqueror. Konqueror shows a error message "Die Echtheitsprüfung des Servers (www.gmx.net) ist fehlgeschlagen. Das Zertifikat der Beglaubigungsstelle ist ungültig. Dem Zertifikat der Haupt-Beglaubigungsstelle kann zu diesem Zweck nicht vertraut werden. Das Zertifikat kann aus internen Gründen nicht überprüft werden." Translation: Authentication checking of server (www.gmx.net) did not succeed. The certificate of the certification-authority is invalid. The certificate of the main authority cannot be trusted. Due to internal reasons the certificate cannot be validated." The same certificate is accepted by Mozilla Firefox.
Konqueror isn't able anymore to validate any certificate - you have to decide for yourself if you want to accept a certificate. How do other browser handle that? They seem to countercheck the certificates somewhere.
Is this still the case in the latest version of KDE, v4.7 or higher. The certificate database might have been updated to include that particular one.
Cannot reproduce in latest version of KDE, v4.9.1. Feel free to reopen if that is not the case for you.
This is one of the most annoying KDE bugs. It's still present in latest KDE versions.