Publication 52 - Hazardous, Restricted, and Perishable Mail > Appendix C > USPS Packaging Instruction 3D
Certain limited quantities of flammable liquids and solids containing ethyl alcohol are permitted in the domestic mail via air transportation, with special authorization from the director, Product Classification, when all applicable requirements in 343.25 are met.
For content not more than 70% ethyl alcohol:
Labels and markings must be placed on the address side of the mailpiece unless specified differently in 221.1 and 325.1.
For content more than 70% ethyl alcohol: