It's configurable, as you say. Maybe I don't understand your argument "at least you won't be MITM'ed". Almost nobody runs SMTPS anyways. I'm just saying that if

It's configurable, as you say. Maybe I don't understand your argument "at least you won't be MITM'ed". Almost nobody runs SMTPS anyways. I'm just saying that if someone decides they want to enforce encrypted SMTP, it really doesn't matter if that is implemented as mandatory STARTSSL vs SMTPS. One is not more suspectible to MITM than the other.