In my experience (europe) delivery companies get access to my unique email address that I also only use to buy things on amazon. They use this email address to send me information about deliveries directly to my inbox.
Are you sure those emails are directly from those companies? I only get messages sent through Amazon forwarding addresses, which exist precisely for the purpose to not disclose your own email address to third parties.
Amazon specifically does not want third party sellers contacting customers through side channels other than Amazon itself, and thus does not typically give out emails directly.
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.
If they actually cared I'm sure there would be a way to report these kind of issues. I got physical mail about submitting review for a product that I bought from Amazon (sold by company X, shipped by Amazon) in exchange for Amazon Gift card. The mail did contain name of the product. I tried to report it and
* 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 have similar, but, in my case, it's because I have an account with the delivery company, and they associate the email with my address, so I get emails, whenever a package is to be delivered at my address, regardless of its origin.
That doesn't seem relevant to the subject of whether or not delivery companies get your address from Amazon, nor to the main topic of an Amazon-only email getting leaked?
But yes, some couriers do let you tie an email address to a physical address to get notifications.
