different email than web server

This is sort of a follow up to my blacklist question. Is it common, or a good idea, to have your client's email routed thru a different company or server than their websites? Like perhaps using a "top notch" company to host your important clients email, like no-ip.com or something of that nature? then maybe using your hosting server as backup somehow? My goal is to have nearly bullet proof hosting and 99.9% bulletproof email. Email is what people complain about the most and is also more difficult to troubleshoot vs. website downtime.

I don't see why you shouldn't host web sites and email on the same server, as long as you have the resources and realize that you're going to need to scale up sooner than if you start off with separate machines.

Colin