Are your users all in one physical, geographic location—all in one building? All on one floor? In one room? Or do you have a global headquarters in St. Louis, branch administrative offices in Tangiers, Barcelona and Oshkosh, and factories in Singapore and Tuscaloosa? In your current email system, how many Exchange servers and users are at each location? After you migrate, how many Sun Java System servers will serve the users at each location?
In your current email system, how are your users assigned to your various Exchange servers? By geography only? By administrative entities within your organization—for example, the Sales Department vs. the Engineering Department vs. Customer Service and so forth? Or by business unit or team—for example, the Product XYZ team vs. the Product ABC team?
What are the education and training backgrounds of your various users? How long have they been working with computers? To what extent are they likely to require administrator or help-desk “hand holding” during the migration?