Listserv is software for managing mailing lists: creating lists, distributing emails over the list, adding new subscribers, and adjusting settings. It can be operated via a Web interface, by sending email commands, or via TCP. liblistserv is the glue between listserv and your C program for manipulating or querying a mailing list. By calling the provided functions, your program does not need to parse the results. Liblistserv is a reentrant library, written in C, meant for communication over TCP with a running Listserv instance.
mailing-lists-sieve is a utility to generate Sieve scripts (RFC 5228) for listserv mailing lists and upload them with the ManageSieve (RFC5804) protocol. The program can be extended to generate scripts for other mailing list managers or upload them by other means. mailing-lists-sieve can integrate into listserv and upload the scripts for the mailing lists when a new subscriber is added or removed from the list.
Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
OpenEMM is a Web-based enterprise application for email marketing, marketing automation, email newsletter, and service email (like transaction email and event and time triggered email). It offers many features for professional users, among them: a great user interface, automatic bounce management, opening and link tracking, a lot of graphical real-time statistics, a content management system, a multi-queue mail backend for maximum sending performance, a plugin interface to easily extend the core functionality, and a scripting feature to enhance the functionality of OpenEMM with triggerable customized actions.
Microbrew Message Center is designed to be an immensely scalable mail platform supporting multiple users, multiple domains, and multiple mail servers. It is akin to iPlanet or post.office but is not as complex and uses open source software to perform mundane services such as Web and mail services.