OpenChange aims to provide a portable Open Source implementation of Microsoft Exchange Server and Exchange protocols. Exchange is a groupware server designed to work with Microsoft Outlook, and providing features such as a messaging server, shared calendars, contact databases, public folders, notes and tasks.

We are working on two different aspects:

1. Provide interoperability with Exchange protocols. This is the MAPI library development purpose (libmapi). MAPI stands for Messaging Application Programming Interface and is used within Microsoft Exchange. The OpenChange implementation provides a client-side library which can be used in existing messaging clients and offer native compatibility first with Exchange server; and in a near future with OpenChange server. Novell Gnome Evolution and KDE Akonadi (KMail, Mailody) are using the OpenChange MAPI library to access Microsoft Exchange servers natively.

2. Provide a transparent replacement to Microsoft Exchange Server with native Exchange protocols support and direct communication with Microsoft Outlook. This basically means that OpenChange server won't need any plugin installation in Outlook. The server is tighly linked to Samba4 since it is developed as an endpoint module for smbd (the samba server daemon) and is part of the mapiproxy project, an Exchange proxy which can act as a transparent gateway and/or progressively and seamlessly replace an Exchange server with openchange.