I'm curious - for those who care about private email services - what do you do about the recipient? Or is the idea to only email those also using things like ProtonMail?
For me, it’s mostly about keeping Google or Verizon (Yahoo) from reading all of my receipts and notification emails to build a marketing profile of my entire life.
The senders of those receipts likely use a provider like AWS SES or otherwise.
Normally email shouldn’t be used for secure communication since it is insecure by default. The best solution is to use email to set up a connection over an encrypted channel (matrix, signal, …)