Comment by fosron

Worked on an ESP. We had a couple of server software we used on low-level for sending. None of them would accept the message without a Message-ID. But even if you have a super-custom, SMTP-injecting service built, how can you ignore all of these bounces from a provider thats likeliest to be the major one you are sending to? Unthinkable. I would not like to have business with such a payment provider.