This blog post by Jonathan Brown suggested replacing SMTP with Ethereum blockchain; specifically, utilizing the log channel to monitor events.
With this approach, emails wouldn't actually be stored within the EVM (Ethereum Virtual Machine) storage, but every email would still be present in the blockchain blocks. The EVM log mechanism would make it simple for a full node to monitor and be alerted whenever an email was submitted.
I don't believe that this would be feasible in the real world, for several reasons
- There are lots of email being sent, some of them quite large
- Most people wouldn't want their emails forever on the blockchain, the future resiliency of GPG is unknown, and GPG encryption does not provide perfect forward secrecy. Once a key is compromised, all is revealed.