I thought this was a pretty cool example of what you can do with Ajax + Exchange + Active Directory. I am no web developer, so expect to find design bugs, and even bugs in the implementation of my own api : ) The security has been heavily scrutinized, however, and you're fine there. It's all open source code anyway, so look for yourself : )

The demo user name and password are 'owa.app'

Be aware that you will have to make certain security allowances. The page explains how to do it and why.

https://web.austin.utexas.edu/akutz/owa.app/

Maybe the Zimbra developers can use some of tihs to make their app integrate on the fly with Exchange...