[Exim] encrypted mailing list?

I'd like to start a PGP/GPG-encrypted mailing list. Anyone know of such a
mailing list which could serve as a model -- and source of manager
software/scripts?

(A user encrypts their message with the list's public key. When the list
manager receives the email, it attempts to decrypt the message. Failures
are sent to me. After successful decryption, for each subscriber's public
key on the manager's keyring, the message is re-encrypted and sent to the
email address(es) on the key. The message is discarded.)

Thanks for any help!

Tod
abl.com