How can I solve the problem showed in the below message?. What deb must I install, or where is the pluging which I must add in the crypto plugin tab?. Note that I have installed the gnupg deb package. "Message was signed with unknown key. The validity of the signature cannot be verified. Problem: OpenPGP plug-in was not specified. Use the 'Settings->Configure KMail->Security' dialog to specify the plug-in or ask your system administrator to do that for you."