using hashcash in mutt
To add hashcash to outgoing mail with mutt, download, install and setup hashcash-sendmail.
You will also need to install the hashcash tool.
Then edit your .muttrc file to add the line:
(or the full path if it is not in the search path).
another mutt hashcash scriptThere is also Tim Ruddick's foreground hashcash filter for mutt. This creates hashcash in the foreground rather than backgrounding a process, and then sends using sendmail.