That's debateable, DOS sure, but you have much greater control and speed of access with a local mail server and past mail will still be accessible during any attack. I wasn't referring to DOS/DDOS-style reliability. In my mind, reliability ~= uptime > 99.999% Of course, you're correct in noting that the fact that a VPS is, by definition, distant from me, means that in case of a network outage or DOS attack, email is inaccessible and therefore a server at home is better in this respect.
So to access your emails when your server is being DDOS'd, you need to sit at home where you are virtually cut off from the Internet. Clearly, in this respect, a VPS is much better as its connection will withstand much larger DDOS attacks than your home DSL.
So in essence, what you're proposing is to only upgrade from VPS to private hosting when the resiliency of my private server is good enough - i.e. not most naive setups? It does make sense, and would make backups more urgent and important. However, at this point these discussions are starting to get academical, as it would take at least a year, if not five, for me to have enough spare time to work. Many thanks, Gesh