qmail fork with IPV6, TLS, DANE, DKIM, SRS2, SPF, daemontools, qmailanalog, mess822, & ucspi-tcp

List of "big mailers" for OpenBSD's 'smtpctl spf walk' mechanism

The Mailismus mailserver - SMTP, IMAP, POP3, SSL

Web interface for SQLgrey built on Laravel 5

gld, a lightweight greylist daemon for postfix

Greylisting of suspicious source (exported from code.google.com/p/gross)

Postfix policy application written in Go

dynamic and optionally distributed greylisting daemon

OpenSMTPd filter for quick and dirty greylisting

Verify email(s) using correct SMTP conversations (HELO / MAIL FROM /RCPT TO)

Haraka plugin that implements greylisting