[Xylakant]

Control as in you get to choose when hardware fails or zero-day exploits get released?

I hear that argument a lot, but you really need to invest a lot of time to provide a secure and reliable e-mail service. It just doesn't pay of in most cases. So yes, you can do it, but don't pretend it's a viable way to save money. I get to see hacked e-mail servers every couple of month.