While the following questions are not applicable to creating your usage profile, they are important to developing your sizing strategy. How you answer these questions might require you to consider additional hardware.
How much redundancy do you want in your deployment?
For example, you might consider high availability. Consider how much down time is allowed, and if you need clustering technology.
Do you need a DMZ to separate your internal and external networks? Are all users using the internal network? Or do some of them connect by using the Internet?
You might need MMP proxy servers and separate MTA layers.
What are your response time requirements? What are your throughput requirements?
What is your specific criteria for resource utilization? Can your CPUs be 80 percent busy on average? Or only at peak?
Will you have messaging servers at different geographic locations? Do you expect users’ mail to be located geographically?
Do you have archiving requirements for keeping mail messages for a certain length of time?
Do you have legal requirements to log all messages? Do you need to keep a copy of every message sent and received?