The author's definition of what makes a "decentralized application" is too strong and I don't agree that email isn't an example of a decentralized application. She argues that it's not because it's really hard to run your own mail server.
To me, "decentralized" doesn't mean every user has to run their own node. It means it's an open network, anyone can join, and there's no centralized control / censorship. You can buy a domain and use Proton, Fastmail, or any other provider to have your own email. If you become unhappy with them, it's easy to move. We have open specs that allow every service to interoperate, so you don't need to know or care what provider your recipient is using.
To me, "decentralized" doesn't mean every user has to run their own node. It means it's an open network, anyone can join, and there's no centralized control / censorship. You can buy a domain and use Proton, Fastmail, or any other provider to have your own email. If you become unhappy with them, it's easy to move. We have open specs that allow every service to interoperate, so you don't need to know or care what provider your recipient is using.