CAKE (Key Addressed Crypto Encapsulation) is a bunch of Python and C++ for implementing the CAKE protocol. The CAKE protocol is a protocol in which all messages have source and destination addresses that are public keys. This is in the same way that IP packets have a source and destination address that is an IP address.
Coherent Mail Gateway is intended to be a very easy to set up MTA using SMTP and POP3. Greylisting is used on the SMTP daemon to reduce spam. In addition, quite a lot of checks on the validity of information from the SMTP client (such as claimed server name and sender) are carried out, and anyone caught telling lies is disconnected. Grey-, black-, and white-listing are supported, as well as (optionally) ClamAV and Spamhaus. The target market is users with static IP addresses. Others can use the system, but its value will be limited to outgoing email.
IVS Milter is a virus, spam, and content milter. It makes use of the antivirus package ClamAV, and can also seamlessly integrate SpamAssassin (either spamc or libspamc). IVS Milter is also plugin based and currently supports virus scanning, spam scanning, content-type matching, attachment type matching, and attachment filename matching.
The Gordano Messaging Suite (GMS) is a highly flexible and reliable suite of messaging products. Customers can choose which components meet their needs from email, Webmail, collaboration, instant messaging, calendaring, SMS, and list server software all of which can be complimented by high level anti-spam, anti-virus, and archiving options.
Quotient is multi-protocol (SMTP, POP, IMAP, SIP, HTTP, Q2Q) server that helps with all your online conversations, be they over email, IRC, IM, mailing lists, or voice over IP. It is written in Python on the Twisted framework, and uses Xapian for search and SpamBayes for spam classification.
The inline_smtp Perl script was created to allow filtering of incoming mail on a separate server that houses the mailspools without running a full-blown MTA. While it's possible to configure another MTA, e.g. postfix, to relay all mail to a smart host and do filtering through postfix, the queue can get behind easily, and on a busy host thousands of messages can get queued in a few hours causing delays in delivery from a few minutes to several hours. By filtering while redirecting, mail arrives without any delays, and can be filtered by a seperate host adding headers or content reducing the load on the final mail host.
DynamicRelay prevents your customers from sending spam, and authenticates users using POP or IMAP to send email in a pop-before-smtp fashion. You can use it with the wu-imap, dovecot, Courier, and Qpopper IMAP/POP servers, and with Postfix or Sendmail. You set the limit to the number of email messages a user can send per day. This is useful when you have users infected by viruses that send thousands and thousands of spam messages, or who send spam deliberately. You can also control how long users are allowed to send email after their last POP or IMAP authentication. Abuses are logged and emailed to you, and you can put your own static entries in the access file.