When sharing Controlled Unclassified Information (CUI) through email, the required markings are:
- A banner marking with the acronym "CUI" must appear at the top and bottom of the email body.
- The banner marking must be carried forward when forwarding or responding to emails containing CUI.
- The subject line of the email may include an indicator such as "CUI" or "Contains CUI" to alert recipients.
- A CUI Designation Indicator (DI) block, which identifies the agency controlling the CUI, must be included after the sender's signature block in the email.
- Attachments containing CUI must be identified with appropriate markings and must be encrypted.
- The name of attached files may also include a CUI indicator.
- Emails containing CUI must be encrypted to protect the information.
Additionally, if an email is only a transmittal for a CUI attachment and does not itself contain CUI, the DI block is not required in the email body, but the first and last lines of the email should still indicate "CUI" and a statement such as "This email is unclassified when CUI Document is Removed" should be added. These markings help ensure proper handling and protection of CUI transmitted via email, consistent with government regulations on CUI dissemination and safeguarding.
