FreePOPs is a webmail to pop3 conversion daemon. It is extensible to support other webmail using the scripting language LUA. See the homepage for supported webmails.
libmail is a C library intended to help programmers when adding mail checking and retrieving capabilities to their applications, supporting popular mail protocols like IMAP and POP3 as well as *nix-like mailboxes.
Your own mailing system (most easiest to use with zero configuration) for the entire world (available in almost all the languages of the world) which will include Mail User Agent and Mail Transfer Agent thus trying to give maximum speed while transferrin
HIndi Mail Client in Java, can be extended as a editor and a plugin on web pages to mail and view mails in Unicode Devnagri Font. The Mail Client could be used to embed into a HTML page so that people need not install it to view and recieve mails.
Virtual Qmail - virtual domains management system for qmail. It is designed to be fast, reliable, and easy to use. Includes software allowing users to manage their accounts via WWW.