USPS Homepage

22 Marking Requirements

221 General

Hazardous materials and restricted or perishable matter, unless specifically excepted in 222, must be clearly identified on the address side of the mailpiece, including the name and address of both the mailer and the addressee.

When required, the contents also must be clearly identified on the address side. The contents must be disclosed to be mailable. A mailability determination may be required based on the mailer’s disclosure concerning the contents at the time of mailing.

Other markings required by the Postal Service or other federal regulatory agencies also must appear on the address side of any mailpiece containing hazardous material, restricted matter, or perishable matter. Required markings must be applied with a nonsoluble material or other material that cannot be rubbed off or smeared.

Mailers should ensure that their packages meet all applicable labeling and marking requirements to avoid rejection of the mailpiece by Postal Service acceptance personnel or air carriers.