NIST Special Publication 800 -177 Revision 1 Trustworthy Email Scott Rose J. Stephen Nightingale Simson Garfinkel Ramaswamy Chandramouli This publication is available free of charge from: https://doi.org/10.6028/ NIST.SP.800 -177r1 C O M P U T E R S E C U R I T Y NIST Special Publication 800 -177 Revision 1 Trustworthy Email Scott Rose J. Stephen Nightingale* Advanced Network Technology Division Information Technology Laboratory Simson L. Garfinkel US Census Bureau Ramaswamy Chandramouli Computer Security Division Information Technology Laboratory *Former employee; all work for this publication was done while at NIST This publication is available free of charge from: https://doi.org/10.6028/ NIST.SP.800 -177r1 February 2019 U.S. Department of Commerce Wilbur L. Ross, Jr., Secretary National Institute of Standards and Technology Walt er Copan, NIST Director and Under Secretary of Commerce for Standards and Technology Authority �is publication has been developed by NIST in accordance with its statutory responsibilities under the Federal Information Security Modernization Act (FISMA) of 2014 , 44 U.S.C. § 3551 et seq. , Public Law (P.L.) 113- 283. NIST is responsible for developing information security standards and guidelines, incl uding minimum requirements for federal information systems, but such standards and guidelines shall not apply to national security systems without the e xpress approval of appropriate f ederal officials exercising policy authority over such systems. �is guideline is consistent with the requirements of the Office of Management and Budget (OMB) Circular A -130, Section 8b(3), Securing Agency Information Systems, as analyzed in Circular A -130, Appendix IV: Analysis of Key Sections . Supplemental information is provided in Circular A-130, Appendix III, Security of Federal Automated Information Resources . Nothing in this publication should be taken to contradict the standards and guidelines made mandatory and binding on f ederal agencies by the Secretary of Commerce under statutory authority. Nor should these guidelines be interpreted as altering or superseding the existing authorities of the Secretary of Commerce, Director of the OMB, or any other f ederal official . �is publication may be used by nongovernmental organizations on a voluntary basis and is not subject to copyright in the United States. Attribution would, however, be appreciated by NIST . National Institute of Standards and Technology Special Publication 800- 177 Revision 1 Natl. Inst. Stand. Technol. Spec. Publ. 800- 177 Revision 1, 128 pages (February 2019) CODEN: NSPUE2 This publication is available free of charge from: https://doi.org/10.6028/ NIST.SP.800 -177r1 Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. �ere may be references in this publication to other publications currently under development by NIST in accordance with its assigned statutory responsibilities. �e information in this publication, including concepts and methodologies, may be used by f ederal agencies even before the completion of such companion publications. �us, until each publication is completed, current re quirements, guideline s, and procedures, where they exist, remain operative. For planning and transition purposes, f ederal agencies may wish to closely follow the development of these new publications by NIST . Organizations are encouraged to review all draft publications during public comment periods and provide feedback to NIST. All NIST Computer Security Division publications , other