Ask HN: How to accelerate the adoption of secure email?

Google Chrome accelerated the adoption of TLS for websites by making it difficult to access websites over insecure channels. This is likely because of their dominant market position. LetsEncrypt also commoditised the certificate business to the point of free.

What would it take for a similar thing to happen for unsigned and unencrypted e-mail? Which companies or organisations could contribute to a fast change?