> > Google apps is good but customer wants an on-premise solution.
> IMO, he will also need an on premise sys admin, if this email server
> is facing the Internet.
Exactly. Why bother going around setting up things on your own when you are
getting it for free. Not only you'll save on sysadmin overhead as Arun
said, but also infrastructure cost and time.
Having said that, you may have your constraint and customer specifications
to work with. You could at the least suggest this to them and then make a
choice on technology. I have a related article on this at