using hashcash with TMDA
There are two alternate sets of instructions for using hashcash with TMDA.
using hashcash tool
See TMDA hashcash HOWTO. This approach supports both incoming and outgoing hashcash support. Note it blocks on outgoing sends until the hashcash has been computed. You can avoid the blocking on outgoing send by using the hashcash-sendmail approach described below.
See instructions under TMDA on Kyle Hasselbacher's hashcash-sendmail page.