[LinuxBender]

Email is already designed to be decentralized. You can have a very large number of mail servers in any number of clouds behind multiple MX records, Anycast IP's, Load balancers, etc... The scale of distribution required to defend against these attacks is possible, but prohibitively expensive. Some VPS providers do support Anycast so in theory you could dynamically spin up tens of thousands of inbound MX nodes that would at least spool the emails. Anycast will allow you to have any number of MX servers appear as one IP address. Those nodes in turn then need to relay that to your centralized servers. This brings up more scalability issues as you could essentially DDoS yourself in this pattern. There may not be enough clouds to support this idea and the cost would give just about any CTO sticker shock or medical issues.

If you mean distributing the destination servers that people access that is basically the same pattern. One could in theory spin up cloud instances of the email httpd/smtpd servers but there are still diminishing returns. This also requires the clients to know how to route to the right clusters of servers. Not easy, but doable. Ultimately this is the same problem people run into with web servers hosted on AWS. You can spin up more instances but there are still network link bottlenecks going into each region. AWS and the like have partnerships with scrubbing centers. This model breaks down if the attacker is willing to spend more than $500. Most massive scale attacks cost less than $200 on the dark web. If the extortionists believe they can get more than say $1k, then they might be willing to spend enough to even take down some scrubbing centers. It can cost hundreds of millions to defend against a $200 attack.

The current email RFC's would not support something like crypto/blockchain. At that point you are basically inventing a new standard and adoption may take a very long time unless there is a compelling business advantage to it in my opinion.