see also gnus instructions
Gnus (emacs newsreader) manual entry on enabling hashcash
The below instructions are similar and include both enabling gnus support and support for RMAIL and other emacs MUAs.
using hashcash in emacs
Emacs has a number of mail (RMAIL) and news (gnus) packages. There is an emacs extension hashcash.el by Paul Foley that hooks creating hashcash on outgoing mail for these mail/news systems.
You will also need to install the hashcash tool if it is not included with your distribution.
Download the emacs hashcash.el file.
InstallCopy hashcash.el into your site-lisp directory /usr/share/emacs/site-lisp.
Configureappend the following to your .emacs file: