Postal Explorer > Publication 417 - Nonprofit Standard Mail Eligibility > 4 Qualified Mailings > 4-4 Postage Liability

4-4 Postage Liability

If the USPS determines that a mailing was ineligible for the Nonprofit Standard Mail (nonprofit) rates claimed at the time of mailing, it may assess the organization or any party that entered the ineligible material the difference between the nonprofit rates paid and the applicable regular rates.