spmfilter is a mail filtering framework. It attempts to be a general filtering framework for any purpose. The API enables spmfilter plugins to access messages as they are being processed by the MTA. This allows them to examine and modify message content and meta-information during the SMTP transaction. Plugins are loaded at runtime and can be processed in any sequence. The processing chain can also be altered by a single plugin, for example if the plugin has to stop further processing.
Postoffice is a simple SMTP mail server and client written with spam blocking in mind. It provides a greylist to slow down the rate of incoming spam, and can be configured to do antivirus checking on incoming mail either via the sendmail milter protocol or a traditional hard-coded AV program. Postoffice can be configured to deliver mail to accounts inside vm-pop3d-style virtual domains, and it can further be enabled to support AUTH LOGIN for people inside virtual domains, so they can use postoffice as a mail forwarder when replying to mail. Postoffice accepts (and ignores) many of the same command line options that are passed to sendmail, and it comes with the usual crop of sendmail compatable aliases; runq, mailq, newaliases, and sendmail.
Vanguard provides enterprise class anti-virus and anti-spam protection to multiple internal mail servers, including the Gordano Messaging Suite, Microsoft Exchange, and IBM Lotus Notes/Domino. Dual anti virus scanning engines provide both traditional signature based virus protection and advanced Zero Hour protection. Any number of internal servers can be protected from a single Vanguard server. Each of those servers may be servicing the same Internet domain, separate Internet domains, or even multiple Internet domains on a single server. There is no limit to the number of protected domains or message throughput.
hermes is a generic, transparent and multi-platform anti-spam SMTP proxy that uses a combination of techniques (like greylisting, throttling, DNS white/blacklisting, SPF, etc.) to stop spam from reaching your mailbox. Many mailboxes see a 98% spam reduction with no false positives, as hermes is not filtering email based on content, but on strict adherence to the SMTP standards. It's also compatible with most SMTP extensions like STARTTLS (for SSL security) and SMTP-AUTH (for user authentication).
smtpd is a lightweight mail server whose sole purpose is to receive incoming messages and deliver them to local users. Its main "feature" (or non-feature, really) is to be completely unable to relay messages to adjacent servers: if an incoming message is not addressed to a local mailbox, smtpd will reject it. Another convenient feature is its automatic grey-listing of clients that allows you to efficiently reject spammers based on their behaviour. It can handle incoming email traffic for an unlimited number of domains (i.e. act as a MX for these domains) without the need for any configuration (other than creation of users' mailboxes).
libspawner implements the MTA side of Sendmail's Milter (mail filter) protocol that is used by the MTA to delegate policy decisions to external daemons. The main purpose of this library is to enable other MTAs, or any mail-handling software, to talk to the existing mail filters that have been developed for Sendmail.
Open5066 is an implementation of the NATO NC3A STANAG 5066 protocol stack for HF radio communications. It aims to implement all of SIS (Annex A), DTS (Annex C), and some of the application layer (Annex F) functionality such as HMTP. The concrete embodiment of Open5066 is the s5066d daemon.
dkimproxy is an SMTP proxy that signs and/or verifies Domain Keys Identified Mail (DKIM). It is designed to work with Postfix. It comprises two separate proxies: an "outbound" proxy for signing outgoing email, and an "inbound" proxy for verifying signatures of incoming email. With Postfix, the proxies can operate as either Before-Queue or After-Queue content filters.