Email systems such as Microsoft Exchange and Lotus Notes are both the application and database layers and are therefore predictable from one deployment to another. Variations tend to come down to degrees of load by capacity and number of users, which can be easily determined via MiTrend sizing analysis.
In general the single most important requirement is deep application integration. Administrators tend to manage infrastructure resources via their native tools like SCOM or via PowerShell scripts. Additionally, the ability to integrate directly with the email system in order to provide array integrated backup or database-repurposing operations via array snapshot methodologies is critical. Beyond that, these workloads act like traditional transactional workloads and require a combination of low latency in addition to low $/GB and $/IOPS. Additionally it needs to do this while being able to scale from moderate to heavy loads all the way down to very small workloads seem in much of the SMB space where Microsoft still dominates the data services layers. For these reasons, the scale-up/down architecture is the correct architecture choice for this workload.
The Spiderchart below shows the distribution and weighting of the primary workload requirements for this use case.