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.
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.
maildir-bulletin takes a message on standard input, i.e. it runs in the same fashion as a mailing list program, and puts the message in every user's Maildir. The message is created once and links are created from all user's Maildir's to the original. This saves greatly on disk space usage and time. Delivering a 1K message to 100,000 users should only take a few hundred K of disk space and take ten or twenty minutes. If you have an alias to expand to 100,000 users the same 1K message will take 100M of storage and take several hours.
GNU Mailman is software to help manage email discussion lists and e-newsletters. Its integrated Web interface provides easy-to-use access for list members and list administrators. Mailman supports built-in archiving, automatic bounce processing, content filtering, digest delivery, spam filters, topics, Usenet gateways, and more. It is fully internationalized, and supports digests and email commands. It runs on any Linux or Unix-like operating system and is compatible with most email and Web servers, mail readers, and Web browsers.
Dada Mail can help you manage a mailing list, offers complete support for safe, closed-loop opt-in subscriptions, sends out mass mailings, keeps an archive of your messages, and allows you to share your messages in many ways. It runs on your Web hosting account and you interact with it through your Web browser, making it available anywhere you have a connection to the Internet. You do not have to rely on a third-party list management system with costly monthly fees. It is rich with features, but tries to keep it simple. It is designed to favor flexibility, extensibility, and ease-of-use over core speed or extremely flashy but hard-to-use features. It is designed to be installed, set up, and understood by regular people who have Web sites, but has enough advanced features to entice more proficient users. If you've ever installed a bulletin board or blog software, you should be able to install Dada Mail without too many problems. Dada Mail can scale. You can install Dada Mail on most any basic hosting account and start sending out messages. If your mailing list grows large, you can switch to sending with a more powerful third-party system, like Amazon SES, where there's potentially no limit on the number of emails you may send, all without having to change mailing list management systems or your hosting.
phplist is a mailing list and newsletter manager that allows posting via a Web page. It works well when used for announcements, and can handle very large email address lists. Users can sign up to multiple lists, but will only receive a single copy of cross-posted messages. When signing up, users can identify their geographical location, and messages can be targetted to these. You can add place holders in your email that will be replaced with personal details (such as the person's name). Users can update their own information, and unlike many other mailing list systems, they can change their email address. HTML emails are supported.