How does paying ensure the data is your own?

Paying means that the provider doesn't have to mine your email for keywords in order to display targeted ads (yeah, I know Google theoretically stopped doing this recently). So perhaps "your own" in the sense that another entity isn't accessing it.

> So perhaps "your own" in the sense that another entity isn't accessing it.

Do they have a spam filter? If yes, how do they filter emails without accessing it?

You're the customer, not their product.

But the data is still not in your control. Right?

Protonmail has paid plans.