Version: (using KDE 4.2.2) Installed from: Gentoo Packages There are lots of e-mail-senders out there that specify application/octet-stream as MIME type for all attachments they send, regarless of the true file type. KMail now cannot see what to do with this file and does not offer any preferred application. In case of PDF files, I always have to select okular manually when receiving such messages. But the file extension is .pdf, so KMail should guess the MIME type according to the file extension when no usable MIME type is specified by the sender.
Kmail needs a better way to find the type of an attachment. The first step could be to use the filename (including the part after the dot), or use the same method as the file command uses. *** This bug has been marked as a duplicate of bug 199537 ***