# Forbidden materials, see 49 CFR 173.21 · USPS — Mailing and air-carriage restrictions by item category

For Forbidden materials, see 49 CFR 173.21 · USPS, item category is Forbidden materials, see 49 CFR 173.21; carrier is USPS; restriction type is prohibited; scope is domestic mail (air and surface); conditions is Listed as Forbidden in the Pub 52 Appendix A mailability guide; Prohibited in domestic mail by air and by surface, recorded from its source on 2026-08-10.

- **Item category:** Forbidden materials, see 49 CFR 173.21 _(verified: appears in the quote below)_
- **Carrier:** USPS _(our reading, not quoted from the source)_
- **Restriction type:** prohibited _(our reading, not quoted from the source)_
- **Scope:** domestic mail (air and surface) _(our reading, not quoted from the source)_
- **Conditions:** Listed as Forbidden in the Pub 52 Appendix A mailability guide; Prohibited in domestic mail by air and by surface.

## What the source says

> Forbidden materials, see 49 CFR 173.21 Forbidden Prohibited Prohibited Prohibited Prohibited

## Source

- https://pe.usps.com/cpim/ftp/pubs/pub52/pub52.pdf

Last verified: 2026-08-10. Review by: 2027-08-10.
Part of [Mailing and air-carriage restrictions by item category](https://referencesource.org/shipping-restrictions-by-class/).