950 CMR, § 49.06
A voter must provide a letter to the registrar from the director of the shelter stating that the voter is a resident in order to qualify for confidential registration. The confidential voter must the nannually (within one year and 60 days from the previous letter) provide a letter from the director of the shelter in order for his or her registration to remain confidential. The letter from the director shall not be a public record. Should the voter choose to allow his or her confidential registration to expire by failing to provide evidence of residency in a shelter, the voter's name only becomes a public record. The address of the shelter does not become a public record at that time or any other. Under no circumstances shall the address of a shelter be disclosed to any person.
950 CMR, § 49.06