Suppose that beyond confirmation that you actually received and looked at the email, they don't learn a lot. Might be they aren't even interested in identifying the receiver, just some rough estimate on whether they're able to pierce through spam filters.
More interesting hints might be in the accompanying text. What kind of content was used to lure you into amazon.co.jp? What was the sent-from / reply-to info?
My impression is that spam is usually unsophisticated and amateur. They intentionally raise transaction costs by looking inauthentic, to weed out wary victims because those will just be a pain when they finally need to trick them into believing they should pay $10,000 to receive a million.
Yep good points. So they send it from some variant of my name like "promising-eric@amazon.co.jp" (feels similar to using the same area code for a spam call). There's no explicit reply-to. Based on the translations it's one of those "your card failed to be used for a purchase" type emails.
I think your idea of it being a rough estimate seems simple and likely.
More interesting hints might be in the accompanying text. What kind of content was used to lure you into amazon.co.jp? What was the sent-from / reply-to info?
My impression is that spam is usually unsophisticated and amateur. They intentionally raise transaction costs by looking inauthentic, to weed out wary victims because those will just be a pain when they finally need to trick them into believing they should pay $10,000 to receive a million.