I am doing it for 10 years, with almost 0 downtime, also smtp server that hands over mail to your server will retry and wait so - no, it doesnt need to be up 2

I am doing it for 10 years, with almost 0 downtime, also smtp server that hands over mail to your server will retry and wait so - no, it doesnt need to be up 24/7. Actually rejecting email with try later is a way of fighting spam. Also with a $100 worth UPS, raspberry pi lasts forever. And pi is all you need.