or just lease servers from a "dedicated hosting" company. you get all the benefits of a colocated server (customizability, security, performance) and you can let them deal with hardware failures, upgrades, and obsolescence.
I'm in love with Rackspace Cloud stuff and their support, and will end up saving thousands while providing my clients with a state of the art email system and more redundancy. Plus, with their cloud servers I can replicate and backup easily.