Tumgreyspf can optionally greylist and/or use spfquery to check SPF records to determine if email should be accepted by your server.
SPF is information published by the domain owner about what systems may legitimately send e-mail for the domain. Greylisting takes advantage of spam and viruses that do not follow the RFCs and retry deliveries on temporary failure. We use these checks as part of our mail system and have seen several orders of magnitude reduction in spam, lower system load, and few problems with legitimate mail getting blocked.
Tumgreyspf uses the file-system as it's database, no additional database is required to use it.
This man page is a place holder for whoever wants to write a doc to this. Feel free to send it to the upstream Sean Reifschneider <email@example.com> or to me, the Debian maintainer, Thomas Goirand <firstname.lastname@example.org>.