pgpenvelope is an interface to meld using Pine with GnuPG, the GNU Privacy Guard. It allows one to sign/encrypt/decrypt/verify one's mail messages using GnuPG from within Pine. Ease of installation and use, and a nice interface are primary goals during development.
In addition to being just a Pine filter, pgpenvelope tries to maximize the use of procmail so that signed messages only need to be verified only once.