Hi There I am looking to run Exchange in a hosted environment were i can have Exchange connect to multiple domain controllers of my customers and be able to connect and authenticate their useraccounts. I do not want to run it on a separate AD infrastructure. Is this at all possible?

As far I can understand you want a exchange server to authenticate with DCs in mulitiple ADs. I dont think its possible.Vinit Nair MCSE | MCITP - Exchange 2007 "Sanity and happiness are an impossible combination."

You can go for Hosted Exchange Solution. http://www.microsoft.com/exchange/en-us/exchange-online-hosted-email.aspx?Wt.srch=1&WT.mc_id=1171 It will take time to migrate the users bu you can host as many as company you want on the hosted server. You can build your own and co -locate the server but it has different licensing scheme. Hope that helps.Where Technology Meets Talent

As far I can understand you want a exchange server to authenticate with DCs in mulitiple ADs. I dont think its possible.Vinit Nair MCSE | MCITP - Exchange 2007 "Sanity and happiness are an impossible combination."

Short answer. No. Exchange requires its own AD domain. You cannot have Exchange without its own AD. You would then have to setup trusts if you wanted to use authentication from customer domains. However if you are trying to setup the same system that Office365 has with mixed environments, then you are going to be out of luck. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.