COMDOM Antispam is a high-capacity platform designed for the requirements of ISPs and other large organizations that must fight spam. COMDOM is a powerful anti-spam system operating as a stand alone mail gateway with relay control, authentication, and load balancing support. The system consequently can be used together with mail servers or as a stand alone gateway for several mail servers. The robustness, flexibility, and the high data throughput capacity of COMDOM Antispam allow for the software to be deployed for a range of solutions.
perl-esmtpd is an antispam, antivirus, and authenticating SMTP daemon. It integrates with qmail, sendmail, stunnel, etc. It's simple Perl, so you can hack it to suit your needs. It supports RBLs, mx on from, bounce evil phrases, virus scanning, etc. It offers: RBL-sytle black-hole DNS checking when not relaying, verification of valid MX records for the MAIL FROM (when not relayin, the ability to use Stunnel for smtps connections and still do RBL checks etc., simple authentication (i.e. PLAIN or LOGIN) for offsite users, and the ability to reject email with certain key phrases. Many other useful features are included.
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.
Rumble is a mail server suite for SMTP (ESMTPSA), HTTP, POP3, and IMAP4v1 with an extensive C/C++ and Lua API for scripting. It comes with support for SSL/TLS, SQLite, and MySQL and has a Web-based administration and Web mail feature. Additional included modules feature greylisting, DNS blacklisting, SpamAssassin support, and dynamic performance scaling as well as a multithreaded structure that allows for clustering of multiple servers for one or all domains. With the Lua API you can create your own new server mailing lists, CRM software, e-marketing, and other extensions within minutes.