Sometimes, instead of a more descriptive message when your listing ends, you’ll receive the following mail:
Someone has purchased the item you put up for sale on the Galactic Trade Network. You will receive your asking price and deposit, less the Galactic Trade Network’s Commission, in one hour. (Or, after an hour, your credits are attached.)
This happens after server maintenance, when the listing details necessary to generate the mail are lost (luckily, the credits will still make their way to you). If you are crafting and listing many items at a time and need to know what sold, avoid having auctions expire during maintenance periods, which are usually on Tuesday mornings and are announced in advance on the official forums.