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.
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.
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.