Section 2.303 - What are DOI's requirements for protecting SSNs in document sent by mail?(a) DOI bureaus and offices may not include the full or partial SSN of an individual on any document sent via mail unless: (1) The inclusion of an SSN on a document sent by mail is required or authorized by law;(2) The responsible program office has conducted the proper assessment and taken steps to mitigate the use of the SSN and any impacts to individual privacy; and(3) The Secretary of the Interior has determined that the inclusion of the SSN on the document is necessary and appropriate to meet legal and mission requirements in accordance with this subpart.(b) Bureaus and offices shall partially redact or truncate SSNs in documents sent by mail where feasible to reduce the unnecessary use of SSNs and mitigate risk to individuals' privacy.(c) In no case shall any complete or partial SSN be visible on the outside of any envelope or package sent by mail or displayed on correspondence that is visible through the window of an envelope or package.