VM is a mail reader written in Emacs LISP for GNU Emacs and XEmacs. It can retrieve mail from local spool files or remotely via POP and IMAP, display and send MIME messages, thread messages, auto-sort messages into folders, and manipulate "virtual folders" of messages matching certain criteria. In Emacs versions with X support it provides an interface with toolbars, menus, and mouse-based message selection.
MIMP is a version of the popular webmail client IMP intended for mobile phones and PDAs. Basic webmail functionality is implemented, including mailbox viewing and paging, viewing messages, deleting, replying, forwarding, and composing new messages. It utilizes the Horde Application Framework.
Mac Mass Mailer is a fully-featured mass mailer that supports message templates and a recipient database. It offers everything you need to create and maintain mailing lists for different needs and send mass messages directly from your computer at a very high speed. It uses Apple Mail's message delivery framework to deliver your messages. The recipient database is fully customizable. You can add as many recipient fields as you want and use them in message templates for the purpose of personalizing your messages.
Claws Mail is a GTK+ based, lightweight, and fast email client. Almost all commands are accessible with the keyboard. It also has many features such as multiple accounts, POP3/SMTP/IMAP/NNTP support, OpenSSL, GnuPG, and LDAP support, a plugin system, spell checking, filtering, Actions, spam and virus filters, an address book, internationalization, and much more.
SendEmail is a lightweight, completely command line-based SMTP email delivery program. If you have the need to send email from a command prompt this tool is perfect. It was designed to be used in bash scripts, Perl programs, and Web sites, but it is also quite useful in many other contexts. It is written in Perl, and is unique in that it requires no special modules, and supports any platform that runs Perl. It has a straightforward interface, making it very easy to use.