Linux may be heading toward World Domination, but there are still plenty of incumbent legacies that haven't been dominated. There's just one way to deal with them.

In geology, the term "competent" applies to hard and useful rock. Climbers prefer competent rock. So do builders. Right now I'm sitting in a Scottsdale hotel, looking at a big example: Squaw Peak, a mountain standing in the middle of the flatness that is Phoenix. Squaw Peak's rocks have proved their competence for 1.7 billion years. Camelback Mountain, Squaw's neighbor to the east, is 300 million years younger. Yet both are near the ends of their lives, slowly downwasting to sand and gravel. In another few megennia they'll be gone. To weathering forces, rocks are just a source of dirt. Squaw Peak and Camelback Mountain are the near-solitary remains of a departed landscape now almost entirely reduced to flat desert floor. Most of the surrounding rock has been blown away or washed to sea by red and brown rivers. Today the nameless mountains and plains of the former Arizona are layers of mud slowly lithifying below the floors of oceans.

This kind of perspective is helpful when considering the existence -- and the persistence -- of certain heavy-duty enterprise platforms and applications. Mainframes, for example, date from computing's Precambrian Era, and have been headed for extinction since its Paleozoic; yet they still persist as irreplaceable building materials for large enterprises of all kinds. IBM mainframes even host smaller virtual computers of the sort that was expected to replace them.

Oracle, around for a quarter century, continues to withstand threatening improvements by MySQL and PostgreSQL. Amazon, Orbitz, EMC and Southwest Airlines all deploy Oracle on Linux. Wim Coekaerts and his team at Oracle are also highly involved in the development of Linux itself (in cluster file systems, for example).

And Oracle isn't the only commercial database with ancient origins that continues to find itself at home on Linux. The other day I was talking with Adam Hertz, the VP Technology Strategy at Ofoto, a company that deploys its services on many terabytes of disk space on Linux servers. After he told me the cool stuff Ofoto was doing with Linux, I asked him which database he was using to manage the huge piles of data on company servers .His answer was Sybase. The reasons were both technical and corporate. The two companies enjoy a good working relationship.

Over the past year I've spent a lot of time looking into the growing independence of IT shops from vendors, and the growth of DIY-IT, or Do-It-Yourself IT. While the DIY-IT trend involves growing independence from vendors, it also involves two other developments: 1) healthier relationships with vendors that understand and embrace Linux and open source; and 2) new products, by both vendors and independent open source communities, that provide interoperabilities that some vendors (e.g. Microsoft with Exchange) don't always welcome.

IT personnel are notoriously reluctant to talk on the record about what they're doing with Linux. Or anything, for that matter. It's been pounded into their heads that talking to the press is specifically not part of their job descriptions. Most are willing, however, to talk off the record, as long as it's not made clear which company is the source of the information.

With very few exceptions, IT folks have been telling me lately that Linux continues to make enormous advances inside their organizations, in nearly every area except the one where Microsoft maintains the same degree of persistence we witness with Squaw Peak. That one exception is Microsoft Exchange. "We can easily see our way to replacing Microsoft Office, and even Microsoft Windows," one executive told me. "But we can't get along without Exchange. If you're looking for Microsoft's real lock-in with enterprise customers, Exchange is it."

It would be a big mistake to dismiss Exchange as just another problem program sustained by Microsoft's monopoly powers. The CEO of a nearly all-Linux technology company recently told me her IT chiefs are seriously looking at Exchange. There are, it seems, some things that Exchange does better than anything else, even though it requires Outlook as its client. Here's what I was told just last week by a top IT guy at a major entertainment company:

Outlook is kick-ass if you want to meet with ten other people. That's great for Windows desktops, but we have Linux desktops as well. Those guys use the Outlook Connector for Exchange from Ximian. I have a Linux desktop too: a dual boot Mandrake; but I can never get it to work with Exchange, mostly because I have to go talk to the guys in black robes running the Exchange server. And they don't make it easy.

You've got to look at the big picture from the long-term perspective. Exchange isn't just email. It's business groupware done right. It's not so totally proprietary as Lotus Notes. And it uses email as the groupware context, which works well for people. Especially the group calendaring. You're in outlook. You want a meeting. You look at people's calendars and set something up. Messages go out. Everybody delegates who has rights to see parts of their Outlook calendars. The whole system works very well.

See, the problem with Exchange is that it's a good product. It's also deeply entrenched inside organizations. In our case it took about two years to set up all the trust relationships and to relieve executives of the need for secretaries. You need think about the sociology of all this, and how important it is.

In other words, Exchange is a competent product. There are lots of increasingly competent competitors that work with Linux -- Bynari, Kroupware, Oracle Collaboration Suite, SuSE OpenExchange, PHPGroupWare, Easygate Workgroup, Stalker CommuniGate, ExchangeIT!, Samsung Contact (leveraging HP's abandoned OpenMail), Bill Workgroup Server (and exchange4linux), SquirrelMail -- but I don't see a huge market rush toward any of these solutions, even when the problem being solved is just getting off Exchange (which many customers want to do, in spite of its virtues). At least not yet. (And if I'm missing something, please tell me.)

So, while Exchange and other useful legacy products continue to withstand the erosive forces of Linux and other open source alternatives, interoperability is the guiding virtue. And if Microsoft wants its Squaw Peaks to continue leveraging their competenceis, they'll agree with their customers about the need for interoperability.

Doc Searls is Senior Editor of Linux Journal. His monthly column is Linux For Suits, and his bi-weekly newsletter is SuitWatch.