That comes down to risk analysis there. These businesses should probably be running their own mail infrastructure and doing exfiltration scanning of all outbou

That comes down to risk analysis there. These businesses should probably be running their own mail infrastructure and doing exfiltration scanning of all outbound messages (which needs them to be in the clear at that point, or at least decryptable by the gateway box). Those sorts of businesses also benefit massively from being able to scan incoming messages for spear phishing and viruses BEFORE they get delivered to the end-user device, something which isn't possible if the business firewall can't introspect the messages which are coming through. I think you're actually making my confidentiality absolutist point for me here. Businesses benefit from being able to analyse mail flow across all their employees and spam/virus/fraud scan incoming messages.