I am pondering ways to communicate with the Ethereum address owners safely. We start from the assumption that we know the Ethereum address and email address of the person (voluntarily reported).
Because I do not want to create yet another instant messaging protocol, people are already using email and PGP is somewhat working, I was wondering would it be possible to
Make users convert their Ethereum private keys to PGP compatible keys (e.g. with a web based client side tool or static HTML/JS bundle) so that they can receive PGP encrypted emails
Send email to users, encrypted with a PGP key derived from Ethereum public key (that is probably picked up from the blockchain from the associated transfer to the address)