7 CFR 322.17: Mailed packages.

(a) If you import a restricted organism through the mail or through commercial express delivery, you must attach a special mailing label (APHIS Form 599), which APHIS will provide with your permit, to the package or container. The mailing label indicates that APHIS has authorized the shipment.

(b) You must address the package containing the restricted organism to the containment facility or apiary identified on the permit (post office boxes are not allowed).

(c) If the restricted organism arrives in the mail without the mailing label described in paragraph (a) of this section or addressed to a containment facility or apiary other than the one listed on the permit, an inspector will refuse to allow the organism to enter the United States.