Earlier quoted context omitted.
Emails in response to you direct action (placing an order) are the very definition of solicited email.
No, emails that you ask to receive are the definition of solicited email. When was the last time the grocery store emailed you confirming that you'd just paid for your groceries?
Amazon can't give you a printed receipt because you are not there, physically. So they send you an email instead.
This is not that hard to understand.