If you want to send by P.O. box, just mail normally, but write the P.O. box as the return address. You don't need to go to the post office to mail from a P.O. box, just to receive mail.
If you use your parent's P.O. box, they will get it first unless you obtain their mail key and get the mail before them. You won't get caught by the post office for doing this, but you might get caught by your parents.
You can get a P.O. box if you're under 18, but they're expensive. Your parents will not be notified, and you don't need their permission, but they *can* forbid the post office from giving you one, if they know that you want one and they don't want you to have one. [ theymos's advice column | Ask theymos A Question ]
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