These scripts implement a scheme similar to Bounce Address Tag Validation,
described in the Internet Draft at
http://www.brandenburg.com/specifications/draft-crocker-marid-batv-00-06dc.html

taggedsenderaddress generates a hashed secret, while verifybounce verifies
one. Note that there's no logic in verifybounce to prevent reuse of valid
hashes before their expiration time. 

MDA's like TMDA offer similar functionality. 

This scheme could be implemented at the SMTP transaction level, with great
bandwidth savings for sites which receive lots of fake bounces.

-- 
Brian Ristuccia