I received a notification from E-junkie saying the following:
This is a notification that the remote download link provided by you for [product name here] is not accessible and user (firstname.lastname@example.org) was served the file from our cache for transaction ID [txn_id here].
To explain this notification, it's necessary to explain how we serve remotely-hosted downloads that originate from your URL (rather than being uploaded to our server). The first time someone downloads such a file, we stream the file from your URL to our Web cache and then to the downloader; this is how we cloak the remote origin of the file and enforce our access and expiration controls. Once this initial download has completed successfully, we retain our cached copy of that download; for every subsequent download, we first check to see if the original copy at your URL has changed, and if not, we simply serve our cached copy to the downloader. This eliminates unnecessary transfer-bandwidth surcharges or limits for both you and us, and ensures the quickest and most trouble-free download possible for the recipient.
Occasionally, your server may fail to respond when we check to see if the original source file on your server is newer than our cached copy of the file, or we may determine the original file itself is no longer present at the specified URL. In that case, our system issues you a notification like the one below to make you aware of that fact, so you can determine if you wish to do anything about it. If you do nothing, our system will happily keep serving our cached copy of the original download file to your buyers.