Email as a managed service

I have just been asked what it would take to provide email as a managed service. Does anyone know of any company currently doing this or any whitepapers that I can take a look at to shed some insight on this?

I’m looking to use Citrix/Microsoft and want to know what is takes hardware/software wise to do something like this. Can Exchange 2000/2003 host multiple domains? What security risks are there? etc…etc… Any help would be greatly appreciated.

Thanks,

Matthew Wade
MCSE, Network Engineer