Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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  A portion of a packet that contains layer-specific information such as addresses.
NIST SP 800-113

  The section of an email message that contains vital information about the message, including origination date, sender, recipient(s), delivery path, subject, and format information. The header is generally left in clear text even when the body of the email message is encrypted.
NIST SP 800-45 Version 2