RFC 822 defined the original Internet Message Format for email.
Published in August 1982, RFC 822 was titled “Standard for the Format of ARPA Internet Text Messages.” It described how email messages should be structured, including header fields such as Date, From, To, Subject, and Message-ID, followed by the message body. Its rules helped different systems exchange readable internet mail.
RFC 822 is often confused with RFC 821, which defined the Simple Mail Transfer Protocol used to transfer messages between mail systems. RFC 2822 later replaced RFC 822, and RFC 5322 subsequently obsoleted RFC 2822. Those later documents preserved and refined the same broad message-format tradition.
Modern email also depends heavily on MIME, standardized separately through a family of RFCs, to carry non-ASCII text, attachments, and multipart content. Thus, RFC 822 is the historically correct answer for the original Internet Message Format, even though current implementations follow later revisions of its specification.