It’s delivering email, there is no way for the receiving site to state a certificate is required anyway. Traditionally it’s just a plaintext connection on port

It’s delivering email, there is no way for the receiving site to state a certificate is required anyway. Traditionally it’s just a plaintext connection on port 25 and using and supporting STARTTLS is optional. I suppose you could write up a way to specify this in DNS but it’d take decades to be implemented and you would have to deal with pushback from the snoops who I’m sure don’t mind they can peep into the email you receive.