Although FISMA doesn’t have specific legal requirements for email disclaimers, it does require federal agencies to implement policies to protect their email systems and ensure the confidentiality, integrity, and availability of information. As such, federal agencies may include email disclaimers to help mitigate risks.
Federal Rules of Civil Procedure (FRCP)
FOIA does not directly apply to private companies, but you may be subject to similar laws that require you to disclose certain information upon request. If you’re sending an email that contains sensitive information, add a disclaimer to inform the recipient that the email is intended for the named recipient only, and that any unauthorized disclosure, copying, or distribution of the email’s contents is prohibited.