KMail: public key error message

On some messages I get the following displayed just after the header: /Message was signed with unknown key 0xA7A33F3FF4BF2568. The validity of the signature cannot be verified. Status: No public key to verify the signature/ Does this indicate that I have not configured KMail correctly? -- "Don't you see that the whole aim of Newspeak is to narrow the range of thought? In the end we shall make thoughtcrime literally impossible, because there will be no words in which to express it." -- George Orwell as Syme in "1984"