The fundamental difference is that iCloud email is based on a 41 year old plain-text open protocol which was designed to be federated and lacks any real security or E2EE built-in.
Agree, but it is a closed service. Hacking for shit-n-giggles is fine. Doing it for security research and bug bounties is also fine. Offering another service (and planning to charge, no less!) that uses that closed service without concent isn't, irresepective of motive or ethics. Ethically, whether you advocate FOSS or not, it is wrong. I'm no Stallman fan, but I admire his ethics here; if it's closed, he won't entertain using a service.
