> If you store data on a hard drive you purchased from Best Buy, do you own that data?

I can plug the Best Buy harddrive into almost any computer/SAN I want to and utilize for the purpose I bought for without any lock in. Using the hard drive for my data requires very little trust in Best Buy's good intentions at the time of purchase and zero trust in the continued existence, technical competence or good intentions beyond that -- it is very unlikely that best buy will find a way to snoop on my data even if they wanted to. Everything will continue to work fully as intended until mechanical failure sets in. Feels like ownership to me.

In your case I rent some box from you which will lose almost all its intended function the moment your company goes bust or I stop paying you an annual fee. Furthermore it seems I am completely at the mercy of your original and continued good intentions as in addition to using your lock-in for a big price hike later you presumably can also snoop on my data. As far as I can tell there is no really substantial trust differentiator to protonmail. I have to trust them when they claim they won't read my email and are competent enough to keep things secure and I have to trust you (and continue to trust you as long as I want to use the device) that you will encrypt my data and not exfiltrate any of it (or the private key), and furthermore that you run your servers securely enough that no third party will. But what is to stop it? The box is running closed source software that you can remotely update anytime you feel like it, right? I have physical access, but since I don't control the software, what use is that?

Maybe I didn't understand something right, but so far this does not feel like ownership to me.

It sounds more like the worst of all worlds: the lock-in and lack of ownership of a proprietary cloud-based subscription service with the added hassle, inconvenience, downtime and costs of babysitting (and supplying electricity to) a cloud server for you, the provider.

> Data from Helm is accessible using IMAP, SMTP, CardDAV, CalDAV, WebDAV on the local network (without requiring our service).

In what ways is that better than running an IMAP client on my laptop and using it to send data via protonmail, using my own domain, and keeping offline copies of everything (with a periodic upload to backblaze or some other e2e encrypted backup solution)? That seems to offer about the same control over my data, but is cheaper, easier, more convenient, has higher redundancy/uptime and if anything less lock-in. It also doesn't require an additional device that has no use beyond adding an additional failure point and cost center that's my responsibility.

> There is a standards-based way of accessing that data just as there is with the hard drive from Best Buy.

Accessing the data is not enough because what you are selling me is not an overpriced and unergonomic hard drive. You are selling me the ability to send, receive and store email (and likely more).

Don't get me wrong, I kind of like the idea of buying a physical box and a subscription service to self host stuff in a way that gives me better control over my data for an acceptable amount of hassle. But that really requires some amount of openness/auditability and interoperability that currently appears to be absent.