on the USPS.COM site

I remember asking at my post office and they told me they had to go surface mail. I totally forgot. I must have that CRS Syndrome Everthing is there I guess if you look hard and long enough.

344.22 Mailable Flammable Solids

The following are mailable:
Flammable solids that are eligible to be reclassed as ORM–D materials are permitted in the domestic mail via surface transportation.
Safety matches (book, card, or strike–on–box) are permitted only in domestic mail via surface transportation.
344.3 Packaging, Marking, and Documentation

The following conditions apply:
Mailable Flammable Solids. The conditions in Packaging Instruction 4A in Appendix C must be followed. Mailpieces containing mailable
Class 4 materials must be plainly and durably marked on the address side with “ORM–D” immediately following or below the proper shipping name (i.e., Consumer Commodity). A shipper’s declaration for dangerous goods is not required.
Safety Matches. The conditions in Packaging Instruction 4B in Appendix C must be followed. Mailpieces must be plainly and durable marked on the address side with “Surface Only” or “Surface Mail Only” and, as applicable, “Book Matches,” “Strike–on–Card Matches,” or “Card Matches.” A shipper’s declaration for dangerous goods is not required.