Also, the time period is important. If a deadline was given and you can't send out your discs in time, the trader will end up sending back your blank discs, and you will have prevented somebody who could have met the deadline from getting the show. Most traders keep shows on their hard drive to make copies, and don't want to keep the same shows on their hard drive forever. A very important part of the above offer is that the trader will accept the first three people that email him. This means that you must get your message off as quickly as pollible.
Some traders pick random requests, and stop accepting requests at a certain time.
When you do reply, it helps to add some of your personality to the request. Even though some traders accept the first x number of people, it helps if you don't treat them as robots. If you don't hear back, that generally means that you didn't get in. Don't fret over it, just keep looking around until you get in somewhere - sometimes it takes a little patience. When you do hear back, you'll receive an email that will probably include instructions and a mailing address.