Encrypted mail preferred. I sign most of my private emails with the GNU Privacy Guard, an open source implementation of OpenPGP. If you want to contact me by email, you can download my public key here or from the PGP keyservers. To retrieve my public key from a PGP keyserver and import it into your public key ring, open a shell and type the following command:
For additional information, you should consult the manual shipped with your GnuPG distribution and visit the The GNU Privacy Guard Documentation, where you can find the GNU Privacy Guard Handbook, which should be the first book to read, in order to get started with GnuPG.