The native protocols are normally called "MAPI", which is slightly misleading, but convenient. There are really two protocols that run over Microsoft Remote Procedure Call (RPC) - one for the message store (the EMSMDB protocol), and one for the address book (the NSPI protocol).
Akonadi is the next-generation groupware infrastructure, currently under development as part of KDE-PIM. Akonadi components communicate using D-Bus (rather than the normally shared library arrangement we normally have within KDE), so to provide "native MAPI" within Akonadi, we need an application that conceptually translates Akonadi D-Bus calls into matching Exchange RPC calls. That would be a lot of work to do from scratch, but fortunately, we don't need to.
There are a couple of applications in the Open Source/Free Software world that have extensive experience with Microsoft RPC - Wireshark and Samba.
OpenChange is a project that builds on Samba (Wireshark is also used for development, but not at run-time) to provide support for the client-side and server-side "MAPI protocols". The client-side consists of two libraries and some command-line applications, and the server-side consists of a server plugin for Samba. Both client and server components rely on Samba 4, which has some architectural changes that really help to build add-ons like OpenChange - certainly it wouldn't be possible to build OpenChange with Samba 3.
The Akonadi resource that I've been working on uses one of the client-side OpenChange libraries to provide access to a Microsoft Exchange server from an Akonadi client application. It will also provide access to an OpenChange server when this is complete. There is a long way to go, but we do have proof-of-concept access to mail and contact information from a Microsoft Exchange server (any of Exchange 5.5, Exchange 2000, Exchange 2003, Small Business Server or Exchange 2007).
The Akonadi OpenChange resource doesn't have much of a GUI, and screenshots of debugging output are pretty boring, but if you use the akonadiconsole demo application, you can see the resource in action.
Note that the folder names are as returned from the server, and all the data in the contact is from the server (created using Outlook 2003 and saved to an Exchange 2007 server). Even the fish image is from the contact created in Outlook.
The Akonadi OpenChange resource can't actually be distributed as a binary at this stage, because of the Samba 4 dependency which introduces a GPLv2 / GPLv3 conflict. I'm confident that will be resolved at some stage in the future though - hopefully for KDE 4.1 which is where Akonadi should become more widely used.
There is still a very long way to go, and (as always) more help is needed in many areas:
- OpenChange could use some development assistance, and much more testing. Assistance with getting the Windows port to work would also be most welcome.
- Akonadi is progressing, but still needs some more work. It would be particularly useful if there were more Models and Views. This can be done without access to an Exchange server.
- I'd love some help with the Akonadi OpenChange resource, especially if you're at all familiar with Outlook/Exchange/MAPI, or Akonadi.
- Akonadi isn't really designed to send mail (of any kind), but we do need to support sending mail over MAPI protocols. That will require changes to the MailTransport classes within kdepimlibs.