Microsoft Exchange compatible server and client libraries
OpenChange is a portable Open Source implementation of Microsoft Exchange server and Exchange protocols. It provides a complete solution to interoperate with Microsoft Outlook clients or Microsoft Exchange servers.
OpenChange client-side library is used in existing messaging clients and is the solution in new projects to communicate natively with Microsoft Exchange and Exchange-compatible servers. OpenChange server is a transparent Microsoft Exchange server replacement using native...
An email client written in Java, C, and C++ which not only allows standard pop/smpt/imap access, but also integrated access to Yahoo!, Hotmail, Lycos, and many others. This is all done without any additional services (such as pop forwarding).