Microsoft has a blog post on Virtualizing an Exchange Server Environment.

Should You Virtualize Your Exchange 2007 SP1 Environment?

Introduction

With the release of Microsoft Windows Server 2008 with Hyper-V and Microsoft Hyper-V Server 2008, a virtualized Exchange 2007 SP1 server is no longer restricted to the realm of the lab; it can be deployed in a production environment and receive full support from Microsoft. This past August, we published our support policies and recommendations for virtualizing Exchange, but many people have asked us to go beyond that guidance and weigh-in on the more philosophical question: is virtualization is a good idea when it comes to Exchange?

Due to the performance and business requirements of Exchange, most deployments would benefit from deployment on physical servers. However, there are some scenarios in which a virtualized Exchange 2007 infrastructure may allow you to realize real benefits in terms of space, power, and deployment flexibility. Presented here are sample scenarios in which virtualization may make sense, as well as checklists to help you evaluate whether the current load on your infrastructure makes it a good candidate for virtualization.

Microsoft’s Exchange team did their homework and gave examples where you would use a virtualized exchange environment.

Small Office with High Availability

Some organizations are small but they still require enterprise-class availability. For example, consider Contoso Ltd., a fictitious company that regards email as a critical service and has several small branch office site(s) consisting of 250 users. Contoso wants to keep their e-mail environment on-premises for legal reasons and they want to have a fully redundant email system. Contoso's users have average user profiles and the mailboxes are sized at 2 GB.

Remote or Branch Office with High Availability

In the early days of Exchange server, organizations needed to place local Exchange servers in remote and branch offices to provide sufficient performance. With improvements such as Cached Exchange Mode and Outlook Anywhere (RPC over HTTPS), consolidating those servers to a central datacenter became the recommended approach. However, in some situations, poor network connectivity to remote offices still requires some organizations to have a local Exchange server. Often the user populations at these locations are so small that it doesn't make sense to dedicate a whole physical server to the Exchange environment. The technical considerations in this scenario are the same as described in the "Small Office with High Availability" scenario above. For an example of how a company used Hyper-V in this scenario, refer to the case study on Caspian Pipeline Consortium.

Disaster Recovery

In order to provide redundancy for a remote site, some organizations may require a Warm Site that contains a duplicate of the primary production Exchange 2007 infrastructure. The intent of this standby site is to provide as near to the same level of functionality as possible in the event of the loss of the primary site. However, keeping a duplicate infrastructure for standby purposes, although useful for high SLA requirements, can be prohibitively expensive for some organizations. In that event, it is possible to provide a virtual duplicate of the entire primary site using Hyper-V. A typical Warm Site configuration utilizing physical Exchange 2007 servers would include one or more servers configured together as a standby cluster and one or more other servers configured as a CAS/Hub server. To achieve redundancy of just the messaging services within the Warm Site, a total of four physical servers would be needed. By contrast, a Hyper-V-based solution with only three physical servers can provide an organization with a Warm Site that includes two Mailbox servers in a CCR environment, as well as and redundant CAS, and Hub servers. Thus, by virtualizing Exchange in this scenario, you can provide a higher level of services to your users while also saving on hardware, power and cooling costs as well as space requirements when compared to a similarly configured physical solution. The following diagram illustrates one such configuration.

Mobile LAN

There are situations in which a company, agency, or governmental department may need a complete network infrastructure that can be deployed to specific locations at a moment's notice. This infrastructure is then connected to the organization's network via satellite or similar remote WAN technology. For example, a non-governmental organization (NGO) may need to react to a disaster and set up local servers to serve an affected community. This subset of servers would need to be completely self-contained and able to provide all necessary server services to the personnel located in the target location.

If you think virtualizing Exchange or other Mail Servers consider these scenarios where Virtualization can make you Greener.