Publication 417, Nonprofit USPS Marketing Mail Eligibility: Nonprofit and Other Qualified Organizations > 5 Cooperative Mailings > 5-2 Eligible Mailings > 5-2.3 Commercial Mailing Agent
A commercial mailing agent (or other unauthorized entity) may enter mail at nonprofit prices for an authorized organization, if the organization can show that the relationship is a legitimate principal-agent relationship.
If a question arises whether a mailing is eligible for nonprofit prices, the authorized organization must provide, on request, documentation of the relationship that includes all contracts between the organization and other parties to the mailing and any other information requested by the Postal Service.
Examples: Acceptable Principal-Agent Relationships