In our classic internet you have a domain name which is totally centralized. Using email is a decentralized solution. You can create and change your email address million times with no cost.
No, using emails is not decentralized solution all data is stored on one or two centralized servers, and I can also create million of domains if I want, including some free domains.
Shut down just one server and all your ''decentralized nodes'' are dead, and even worse than using emails would be usage of mobile phones as some kind of ''nodes'' and you didn't explain how thot would work but it all reminds on that junk Pi network.
There are thousands of email service providers, and it is highly decentralized. No one is forced to use or not use them and no government can shout down all of them. You can use one or some simultaneously and if you do not trust none of them, just run your email server or even better run your freedom box
https://freedomboxfoundation.org/please note that the email is the ONLY neutral, free (non proprietary) and open protocol/technology for communication in the world that its infrastructure is well-established and is accessible all over the glob.