Seconded—perhaps a third-party seller or shipper who's been compromised.
Third-party sellers are typically given an address like <gibberish-hash>@marketplace.amazon.com to which they can reply, and correspondence is then forwarded by Amazon to the actual customer's email.
* there was no obvious way to do it. Closest thing was by reporting issue on product.
* there was no way to show the customer service agent a picture of the mail. Chat did not support sending pictures & they were unable to open imgur link.
* agent recommended me to leave a report it by leaving review to the seller page. I did that and next day review was deleted.
(I must admit I created them approx 100 USD/EUR turnover last year and 20 USD/EUR this year. Sometimes all alternatives are so much worse.)