The "Mail Accessibility and Inclusion for Low-Income Families Act," or MAIL Act, mandates the United States Postal Service (USPS) to provide free post office boxes to individuals who are unhoused or experiencing housing instability. Within one year of enactment, the USPS must issue regulations for this service, requiring eligible individuals to submit proof of eligibility, subject to box availability. This initiative aims to provide a stable mailing address for vulnerable populations. An eligible individual is defined as someone who is unhoused or housing unstable (including homeless or at risk of homelessness) and meets specific financial criteria or receives certain federal assistance. This includes individuals whose income does not exceed the poverty line, or those receiving aid through programs such as TANF, Section 8 housing assistance, Medicaid, SNAP, or WIC. The USPS is authorized to procure additional post office boxes to meet demand. To fund this program, the bill authorizes annual appropriations to the Postal Service, covering both forgone revenue from free post office boxes and the costs of acquiring, installing, and maintaining new boxes. These costs encompass retail space, equipment, and additional staffing. The Postmaster General must also submit an implementation plan within 180 days and subsequent progress reports every five years to Congress.