...The features that make gross stand out from other greylisters are:
- it's blazingly fast
- it's amazingly resource efficient
- it can be configured to query DNSBL databases, and enforce greylisting only for hosts that are found on those databases
- it can block hosts that match multiple DNSBL's
- it can be replicated and run parallel on two servers
- It supports Sun Java System Messaging Server, Postfix, Sendmail and Exim.
An advanced qmail distribution based on qmail-sql which has SMTP, SMTPS, POP3, POP3S, IMAP, IMAPS services, a content scanner, spoofing protections, SMTP AUTH support, SMTP-after-POP/IMAP, PHP5 API, SPF support and much more...