VMware published a very interesting 19-pages paper about Exchange 2003 achievable performances in a ESX Server 3.0.1 virtual machine hosted by Dell hardware:
This paper discusses the performance and scalability of Exchange Server 2003 when it is deployed within virtual machines hosted by VMware ESX Server 3.0.1 on a Dell PowerEdge 6850 server with a Dell-EMC CX500 FC SAN.
The Heavy user profile from Microsoft’s Exchange Server 2003 Load Simulator benchmarking tool was used to simulate the Exchange workload. Results indicated that a uniprocessor virtual machine can support up to 1,300 Heavy users.
Our experiments also show that consolidating multiple instances of these uniprocessor Exchange virtual machines on a PowerEdge 6850 can cumulatively support up to 4,000 Heavy users while still providing acceptable performance and scaling…
Read the whole paper at source.