Firma works as a command line and MTA pipe alias tool that receives an
 email message in its input, grab the encrypted/signed message, re-encrypt
 and send it to each subscriber.

 In the server you just need the script, a keyring with the list keypair
 and two config files. When mail arrives, it is redirected by the MTA to the
 script and it process the message if its properly encrypted and signed.
 No temporary files are written during a message processing and no default
 message archive, so no messages -- encrypted or not -- rest on your system
 in all steps of the process.

 Contact Firma developers using firma at sarava.org, encrypting the message
 using the public key 0xD68AFEDC available at keyserver.noreply.org.