To name an item, you give its directory and its name. The xstuff server contains many safeguards to ensure that it is not monopolized by people asking for large amounts of data. The mailer is set up so that it will send no more than a fixed amount of data each day. If the work queue contains more requests than the day's quota, then the unsent files will not be processed until the next day. Whenever the mailer is run to send its day's quota, it sends the requests out shortest-first.
Some mailers produce mail headers that are unusable for extracting return addresses.
If you use such a mailer, you won't get any response.