A number of people have provided feedback, corrections, and contributions, as indicated in the Revision History. Thank you!
The following are some of the people and groups that have provided tools and ideas to this document, in no particular order:
A lot of smart people who developed the excellent Exim MTA, including: Philip Hazel <ph10 (at) cus.cam.ac.uk>, the maintainer; Tom Kistner <tom (at) duncanthrax.net>, who wrote the Exiscan-ACL patch for SMTP-time content checks; Andreas Metzler <ametzler (at) debian.org>, who did a really good job of building the Exim 4 Debian packages.
Many, many others who contributed ideas, software, and other techniques to counter the spam epidemic.
You, for reading this document and your interest in reclaiming e-mail as a useful communication tool