What must be included in an email that contains classified attachments?

When emails contain classified attachments, it is essential to include the highest level of classification within the email. This is crucial for several reasons. Firstly, it ensures that recipients are immediately aware of the sensitivity of the information they are accessing. By clearly marking the level of classification, it directs proper handling and establishes the need for safeguarding the information in accordance with security protocols. This practice helps prevent unauthorized disclosure and maintains the integrity of the classified materials being shared.

Other aspects, such as providing an explanation of the attachment's content, may certainly aid in understanding, but they do not meet the primary requirement for classification markings. Similarly, while contact information may be useful for communication purposes, it is not a requirement tied to the classification of the data. A disclaimer about sharing might be helpful in terms of legal or procedural caution, but again, it does not address the critical need for marking the classification level. Therefore, the inclusion of the highest classification level is fundamental in ensuring that classified information is treated with the appropriate level of care and awareness.