Bulk Mailer helps speed the delivery of an email message to many recipients using Sendmail. It's best used in parallel with a mailing list manager such as Majordomo. For input, it takes a file of recipient addresses (one address per line) and a message (with headers already attached) to be sent to the recipients. It sorts the recipient list by reversed domain (so similar ones sort together), splits up the recipients into several groups containing no more than N domains each, creates an SMTP envelope for each group of recipients, and feeds each envelope to sendmail.
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.
ezmlm-web is a Web interface for the administration of ezmlm-idx mailing lists. It has user level access control, and allows you to create, modify, and update any mailing list's configuration as well as control the subscriber base. ezmlm-web provides full support for all the features of ezmlm-idx. The interface is template based and can easily be customized or replaced. It is translated into seven different languages. Support for encrypted mailing lists (gpg-ezmlm) is included.
Ecartis (fomerly known as Listar) is a mailing list management program. It has a lot of similarities to Listserv (which was one of its inspirations), but has been written from scratch to support the features and abilities that the authors felt were lacking (or hard to modify/change) in some of the other list management programs available. Its main flexibility is that it is written around a plugin layer (similar to Apache), which allows you to customize and extend the manager in ways that otherwise would be hard.