Understanding and Replacing Microsoft Exchange

Linux by itself provides a formidable set of internet applications for mainframes, which have always needed them. IBM's eServer strategy seemed incomplete without a robust set of internet tools, which it promised to provide to all of its brands. Near the end of calendar year 2000, IBM demonstrated it could host a thousand instances of Linux on a single S/390 mainframe.

Figure 1. One mainframe supports thousands of Linux instances.

Even so, IBM realized that web servers and GNU applications didn't provide a complete value proposition. IBM needed an application that made Linux a host that reached further into mainstream computing. So they made a call on us.

In April 2001, when the sales manager for IBM's zSeries, the new name for the S/390, visited our company, Bynari, Inc., I did not understand his interest. After his visit, I understood it perfectly. Bynari, Inc. became IBM's first Linux Influencer Partner.

Initially, people knew us for making Linux and UNIX clients talk to Microsoft Exchange servers. Looking to broaden our market, I found the “Exchange Replacement HOWTO” by Johnson and Mead (www.bynari.net/whitepapers_howto.html). Using their work as a guide, we built a server for our Linux client and Microsoft Outlook. Our server and its Outlook Configuration Guide caught on with the reseller channel.

We didn't know anyone at IBM when we ported our server code to a Linux instance running on an S/390 Multiprise 3000. Jimmy Lee, then with Equant, provided the resources to see if we could do it. Gary Ernst of Equant configured the S/390 instance of Linux and provided assistance in getting our server to work.

As long as Microsoft Outlook had an Internet Mail Only mode and provided peer-to-peer folder sharing, we had a product that allowed UNIX and Outlook clients to schedule meetings and delegate calendar tasks. Our server scaled nicely, and we mimicked the Exchange global address list (GAL) while providing views of users' free/busy time and a decent administrative interface.

But then Microsoft released Office XP and made major changes in Outlook. Suddenly, our products needed server-side calendaring. We feared the growing appetite of IBM enterprise customers for a low-cost server solution for Outlook might wane. Therefore, we needed peer-to-peer calendar sharing in Outlook's Internet Mail Only mode, or we needed something on the server side.

With the January 2001 LinuxWorld Conference & Expo approaching, IBM continued marketing our server, somewhat blind to the needs of Outlook XP users. I knew we had to do something and do it fast or lose IBM's trust. At that time, the person who best understood the market problem was Roger Luca of Mainline Information Systems.

Fortunately, Roger and I developed a good working relationship. With Roger at the head of sales and marketing, Mainline became the largest reseller of IBM mainframes. They also were our biggest supporter outside IBM. Roger provided us with hardware resources to help us build server-side calendaring into our product, as well as with people to support us if we ran into hardware-related problems.

Imagine having completed an exhaustive year of development. You have trips scheduled for the holidays and other plans. Then you get a call on your cell phone; your boss asks you to attend an important meeting. That's what happened in our shop. I could hear the dread in the developers' voices when they answered my call.

We met on November 7, 2001, to see if we could deliver a server-side calendar solution by Christmas. Mainline had several sales pending, and they needed that functionality. Two of my people agreed to work with me to get the solution.

As the senior developer, I provided the project framework. In theory, a project has a variety of phases and processes. To shorten the project's life, I instituted a three-step approach that called for research, invention and execution. I gave each phase a milestone. So instead of starting with code, we started browsing the Internet and any books we could find.

Following a week of intensive research, we discovered our challenges. We had to figure out how Microsoft's DCE-RFC protocol stored and moved calendar events around. We had to interpret the stored data, provide a format that we could store on an IMAP server and then forward the data to an Outlook client in its familiar schema. We also had to provide access control over those information stores to allow a user to appoint and delegate control over his or her calendar to other users with varying permission levels.

We spent another intense week researching and discovered a consensus. Every expert, newsgroup, Outlook specialist and company that tried said one could not create a Microsoft Outlook calendar store on an IMAP server. Here's how we did it.