---
kind: "section"
citation: "39 C.F.R. § 121.0"
title: "39"
number: "121.0"
heading: "Market-dominant product service standards."
url: "https://uscodex.org/cfr/39/121.0"
---

# §121.0. Market-dominant product service standards.


Service standards in this part are contingent upon proper acceptance before the applicable day-zero Critical Entry Time (CET). Applying the service standards appearing in this part, effective service standards for combinations of 5-digit originating ZIP Codes and 5-digit destinating ZIP Codes can be found in a lookup table at www.usps.com.


## Notes

### Authority

Authority: 39 U.S.C. 101, 401, 403, 404, 1001, 3691.

### Source

Source: 90 FR 10869, Feb. 28, 2025, unless otherwise noted.