I hosted my personal email domain on a Zero for almost 10 years. It had about the same capability as the very expensive (and large) Win NT4 machine we used for our 80-person organization when I started my career in tech. I eventually replaced the Zero with a Raspberry Pi 4, primarily because the Zero’s IO ports are annoying (eg, USB is not hot-pluggable!) An RPi 4 is extreme overkill for personal email but it still idles under 1W and when it fails I can replace the entire machine for next to nothing.

The point of failure for all of these machines has been the SD card. They seem to last 4 years almost to the day. I suppose if I set up a RAMdisk they might last longer, but honestly, for the price of an SD card it’s not really worth my time.