So what happens when you are traveling and there's a power issue or maybe some other connection issue that knocks this box out of service? Looks like you'll be stuck without email until you can physically get back to this box. This isn't a scenario you worry about with regular email.

The challenge with email is that once you give out any mail address to people, you are on the hook to ensure that it's a functional address. Not something you can just try for 6 months and then easily move on from. And if you decide to move on from this service, will the average person be able to easily migrate that custom domain to a different email provider? (Yes, technically this is possible, but can normal users do it easily? Is it part of the service that Helm provides?)