What does RFC 5322 define?

RFC 5322 defines the Internet Message Format, specifying how email messages should be structured. It covers header field syntax, required and optional headers, message body format, and character encoding rules.

Key headers defined include From, To, Subject, Date, Message-ID, and various addressing fields. The RFC specifies syntax requirements, valid characters, and how multi line values should be folded.

RFC 5322 also addresses body formatting, line length limits, and how messages with both headers and body should be constructed. Following these specifications ensures messages display correctly across diverse email clients and servers.