But running an email system that does not connect to the wider internet also ruins the idea of email as a globally reachable address. Everything is a trade-off :-|
True, but I think the days of email as a globally reachable address are already on their way out. It's not exactly unheard of for some people to be unable to send email to addresses hosted by some common mailservers (including gmail) right now.
However, none of my friends use our mailservers exclusively. They also use the internet mail system. But having our own means that we don't have to worry about deliverability issues, spam, or any of the other problems that exist on the public system.
However, none of my friends use our mailservers exclusively. They also use the internet mail system. But having our own means that we don't have to worry about deliverability issues, spam, or any of the other problems that exist on the public system.