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.
GroupOffice is a groupware suite that takes your office online, implementing online collaboration and CRM. It allows you to share projects, calendars, files and email online with co-workers and clients. It is easy to use and fully customizable. It also features synchronization with PDAs and Outlook.
Distributed Checksum Clearinghouse (DCC) is a system of clients and servers that collect and count checksums related to mail messages. The counts can be used by SMTP servers and mail user agents to detect and reject bulk mail. DCC servers can exchange common checksums. The checksums include values that are "fuzzy", or constant across common variations in bulk messages.