On the website go to the Your Account page ("Account & Lists" dropdown -> "Your Account" section -> "Account" link, which goes to https://www.amazon.com/gp/css/homepage.html ) and click "Login & security" to get to it. Same place you'd update your password/etc.
Maps to the account me and will (if configured correctly) put the mail in a folder called folder if such exists.
The reason you might want many accounts with the same email seem many to me if you don't realise that you can create arbitrary distinct emails this easily.
It seems to me like all benefits of the "exact same email, multiple accounts" feature are vastly outweighed by the inconvenience for users simply forgetting that they already have an account, and creating a second one by accident that way.
I mean, even I end up almost creating an account by accident every now and then (mostly on sites using the horrible "signup is the default, login needs one additional click" pattern), and I do so using autofill from a password manager!
Sometimes you can't even contact Customer Services because "your account doesn't exist" (because you cannot feed the correct email address to their customer service site).
Thankfully it's rare, but when it happens it's extremely infuriating.
Gmail supports it. Microsoft does not. Neither does Yahoo/AOL. It likely was not widely supported in the 90s either. It’s a nice hack but it doesn’t solve every problem.
Are you absolutely sure it's two accounts? I am using the same login on two different Amazon sites as well, but I'd call that SSO more so than "two accounts on one email address", since all data is separated by country, but the email and password are the same.
Source: I also had Amazon accounts in two separate countries and witnessed the different phases of global logins being implemented.
It was indeed called "Multiple Accounts, Same Email", though I only heard that term applied to it much later (after the phenomenon of these accounts was identified as a problem that the company needed to resolve). I don't think it was exactly what I'd call a feature, in the sense that I don't think anyone expected users to do it intentionally, so much as it was "We don't want to lose a purchase to someone getting stuck at the login screen".
The Web and its users have evolved significantly since those early days, and resetting a password by email is no longer the barrier it once was. Among other reasons: web users are savvy to the idea of having accounts, which was not true in Amazon's early days; and email is a lot faster and more reliable now.
Allowing multiple accounts to share an email address proved to be a problematic decision later on for a number of reasons. Amazon doesn't allow this any more, at least not from the primary sign-in screen; it gives an "Email address already in use" error.
It was really annoying as I would login on my browser to one account normally, but when I ordered an Amazon stick, it came with a different account from a different region preinstalled and would complain I didn't signed up for Prime.
I ultimately fixed the issues by manually changing the email on each account to a different address, but it was very confusing until I figured out what was happening.
Interestingly, I can't change the password on one account to the password of the other account. The attempt fails. Which is... somewhat concerning.