It’s an email that’s unrecoverable so not usable in many companies.
It doesn’t sound like you understand why someone would want to do email with public key cryptography, it sounds like rather you do not like the idea of doing email with public key cryptography. Being unrecoverable is just the tradeoff there. Again, what do you think the problem described even is? For reference,
The issue, Yen said, is ensuring that the public key actually belongs to the intended recipient. “Maybe it’s the NSA that has created a fake public key linked to you, and I’m somehow tricked into encrypting data with that public key,” he told Fortune. In the security space, the tactic is known as a “man-in-the-middle attack,” like a postal worker opening your bank statement to get your social security number and then resealing the envelope.
I think if you actually acknowledge the problem of trust for propagating public keys as a real one that is worth being solved, it would be hard to argue that blockchain is a bad fit for that problem, because it is not. Trustless, verifiable propagation of data is one of the things it actually offers unique benefits for.
I’m sure there are other reasons to not like the idea, but that’s what I can think off the top of my head.
It might be useful to start by considering the idea itself and what it is saying, instead of looking for arguments to make against it.