I will give you a straight answer from experience, as I see hardly anyone else did.
The letter means that they have confiscated your order and it is up to you if you want to go and pay Customs a visit at JFK. I hope you realize that it's a trap and you are basically walking into getting arrested on the spot.
They can never prove that you ordered the goods, unless you were stupid enough to use your real name, and in that situation they may have a case against you. Look at it this way. I can order a crapload of AS and send it to my neighbors house without them even knowing. Now, can they get arrested for it? Of course not. There is absolutely no proof that indicates they were the people who ordered the goods in the first place.
The letter is just part of the intimidation game that Customs plays in the hope to scare the shit out of you and confess to your wrong doing.
Just forget the letter and try to purchase locally next time. If you purchase through the mail again, I can tell you right now, you are seriously running the risk of getting paid a visit by your local police. At this point, you address has been marked by Customs, and they will pay very close attention to packages on their way to your house.
Dont believe me? Well, it happened to me. I was getting ready for work one morning and I had a knock at the door. Two local police officers came into my house and started asking me questions about people ordering AS through the mail to my address. Now, I knew that they were basically trying to play the intimidation game on me, so I played it cool because I knew they did'nt have jack shit on me. They began to get very pissed off because most people would normally get scared and start to spill their guts. Then they pulled the shit about getting the FBI involved if I did'nt tell them what was going on. I literally laughed in this idiots face and asked them to kindly leave.
Moral of the story: Do not be intimidated. Intimidation is the single most effective weapon the authorities use to get people to confess or give them information they need which can ultimately lead to an arrest, or, evidence that can be used in court.
Just keep your cool.
PS: Dont order through the mail. It really is stupid and I cant believe that many of you guys on the board continue to do so. You're just asking for trouble.
SAF