Section 297.602 - Protecting Social Security numbers in mailed documents(a) Social Security numbers must not be visible on the outside of any package OPM sends by mail or displayed on correspondence that is visible through the window of an envelope or package.(b) A document OPM sends by mail may only include a Social Security number if the Director of OPM determines, on the advice of the Senior Agency Official for Privacy, that the inclusion of a Social Security number on a document sent by mail is necessary and appropriate to meet legal and mission requirements.(c) The inclusion of a Social Security number on a document sent by mail is necessary when- (2) Necessary to identify a specific person and no adequate substitute is available.(d) Social Security numbers must be partially redacted in documents sent by mail whenever feasible to mitigate any risks to privacy.