The original documentation from where this document has been obtained can be found in the man pages from "mutt", "pgp", "pgp5", "gnupg", "procmail", in the respectives directories in /usr/doc and in the world wide web sites:
The recommendations (request for comments, RFC) that are referenced in this document are:
and can be found in /usr/doc/doc-rfc and in various sites in the world wide web, like http://metalab.unc.edu and http://nic.mil. You can get information from RFCs in RFC-INFO@ISI.EDU