Typically, Microsoft Exchange aggressively uses all of the provided memory available in a guest operating system. While vSphere can support memory over commitment, this must be considered with caution to avoid performance impact due to resource contention. For virtualized business critical applications, such as production Microsoft Exchange systems, VMware recommends setting a memory reservation on the amount of memory configured for the virtual machine. Also consider:

The exact number of NIC/HBA ports might vary on each ESXi host. More ports might be required for a successful design depending on the number of virtual machines and customer-specific network and storage requirements. The number and exact design must be determined by a detailed sizing analysis with the VMware Cloud Provider solution architect.