The Mobile Post Office Relief Act would require the U.S. Postal Service to deploy mobile retail units to communities within three business days when a local post office temporarily closes and is located more than half a mile away from any other post office. The mobile units would provide key services that the closed facility previously offered, including retail postal services, mail pickup and delivery for post office box holders, and processing of address change and mail hold requests. The requirement would apply to any post office that has not provided services for at least 60 days and applies equally to Postal Service-operated facilities and contractor-operated ones. For post offices already closed when the law takes effect, the Postal Service would have 30 days to station a mobile unit in the affected area. The legislation contains no new appropriations or specific funding levels, instead requiring the Postal Service to use existing resources to meet these obligations.