greytrapping daemon to complement OpenBSD spamd
greyscanner complements OpenBSD spamd(8) greylisting by applying additional heuristics to greylisted hosts. Additional heuristics include: confirm senders email address is valid, confirm existence of the senders MX or A record in DNS, confirm recipient address(es) is valid, and more. Offending hosts are flagged as 'trapped' in the spamd database.
/etc/mail/greyscanner.conf optional config file
Bob Beck created greyscanner in 2006. Jim Razmus II revised the program, added documentation, and packaged it for OpenBSD in 2009.