Most mailable hazardous materials fall in the ORM–D (other regulated materials) category. ORM–D materials do not require Department of Transportation (DOT) diamond–shaped hazardous materials warning labels. Postal Service regulations do permit the mailing of a few hazardous materials that fall outside the ORM–D materials category. Chapter 3, Exhibit 325a and Exhibit 325b, and DMM 601.10 for more specific information on hazardous materials warning labels and marking requirements.
