Features in this release include encrypting Drupal's outgoing e-mails to the public key of the recipient(s) as well as a simple asymmetric-key encryption/decryption API that under the hood uses GnuPG to perform the operations.
The very latest development snapshot for Drupal 6.x. Recommended for expert users who feel comfortable submitting bug reports for the occasional unexpected glitch.
Note: This is experimental software meant for advanced users; assume nothing works, and you may be pleasantly surprised. And when it breaks, you get to keep both pieces.