Can open source replace Microsoft Exchange?

Even Thunderbird, Mozilla Messaging's answer to Outlook and the most popular open-source e-mail client, has made little progress in denting what's estimated to be Outlook 80 percent plus business e-mail client marketshare. That's because Mozilla has largely neglected Thunderbird in favor of Firefox. Even now, Thunderbird's security fixes tend to lag behind Firefox's fixes, and while Firefox's developers are looking well beyond the current 3.0 version, Thunderbird has only released its second alpha for version 3.0.

Without a viable, open-source e-mail client contender for Windows, Outlook remains businesses' e-mail client of choice—despite Outlook's infamous security problems. Since that's the case, any rival to Exchange has to be able to communicate with Outlook in the same ways that Exchange does and duplicate Exchange's functionality. That's not easy.

Jennings said that open-source developers have tried three different ways to do this. "The simplest way is to run a background task on the PC that does a sync with the mail server, probably using IMAP, and then outputting the result to an Outlook Personal Storage Table (PST) file." Bynari, to the best of his knowledge, is the only program that uses this approach.

Another path to Outlook is to "reverse-engineer Exchange's wire-protocols," says Jennings. In this approach, "you forget about installing software on the desktop and try to make the server look to the client just like Exchange. Outlook really does think it's talking to Exchange. The only server that tries to do that is PostPath.

One advantage to this route is that by not requiring any client-side software, installation and maintenance costs are reduced. While PostPath doesn't have all of Exchange's fancier features, it does work well for providing Outlook with the basics of integrated e-mail, calendar, and contact management.

The most popular approach, though, which is used by both Scalix and Lotus Domino/Notes, is to use a "MAPI plug-in on the client," says Jennings. "This hooks into the MAPI subsystem and then to Outlook. In theory, you're not fooling Outlook, you're using the designed way in to it to talk to an alternative server. The MAPI sub-system, however, leaves something to be desired, because the MAPI documentation was, until the European Commission forced Microsoft to open up its network protocols, a mess."

While many people are aware that the European Commission's decision opened up Microsoft's Common Internet File System (CIFS) and Active Directory protocols to Samba, few have picked up that MAPI was also opened up. There is an open-source project, OpenChange, working in conjunction with Samba to build open-source implementation of Microsoft Exchange Server and Exchange protocols from this information. But, curiously, no commercial company is following up on this work, according to Radicati.

It can only be a matter of time, though, before an existing Exchange-replacement company, or perhaps a new one, starts working with OpenChange. As it is, several Linux distributions, including Fedora and Debian incorporate OpenChange in future editions. OpenChange, while already usable, won't be ready for prime-time though until Samba 4, which will include Active Directory and and Heimdal Kerberos network user authentication is released. Unfortunately, Samba 4 is still in alpha. Even with the opening of Microsoft's protocols, Samba 4 isn't expected to see the light of day in 2008.