Zimbra's CTO, Scott Dietzen, recently posted on his Blog site a short post announcing Zimbra 4.5 in a virtual appliance.  Check it out, along with a recently posted Whitepaper on the topic.

Software appliances promise to augment Software as a Service (SaaS) as an easier, cheaper way to use third-party software, especially by lowering the cost of managing independently changing subcomponents of a software "stack"---application logic, database, web application server, virtual machine, operating system, and so on. For our 1.0 software appliance, Zimbra has teamed up with rPath (think Linux distribution for software appliances), and for virualized deployment thereof, VMware. For a more detailed discussion of our thoughts on software appliances as well as our technical collaboration to date with rPath and VMware, please see our recently posted whitepaper. And for those that would much rather try out our initial bootable ISO or VMware appliance images, they are now posted on Zimbra's standard download pages for the Network Edition, and shortly, for the Open Source Edition as well. Feedback most welcome, either on the paper or, better yet, on the software appliance itself.

Read or comment on his post, here.