---
kind: "unit"
title: "39"
title_heading: "Postal Service"
key: "chI/subchC/part121"
level: "part"
label: "Part 121"
heading: "Service Standards for Market-Dominant Mail Products"
release: "ecfr-current"
date: "2026-08-27"
url: "https://uscodex.org/cfr/39/chI-subchC-part121"
sections_count: 5
---

# Part 121 — Service Standards for Market-Dominant Mail Products

Title 39 C.F.R. — Postal Service › Chapter I — United States Postal Service › Subchapter C — Post Office Services [domestic Mail]

## Sections

- [§121.0. Market-dominant product service standards.](/cfr/39/121.0.md)
- [§121.1. First-Class Mail.](/cfr/39/121.1.md)
- [§121.2. Periodicals.](/cfr/39/121.2.md)
- [§121.3. USPS Marketing Mail.](/cfr/39/121.3.md)
- [§121.4. Package Services.](/cfr/39/121.4.md)