Returns the original message exactly as received, in RFC 5322 (MIME) format, as a `message/rfc822` download. Use it when you need the exact bytes: full headers, signatures, or your own MIME parsing. For parsed fields use [Get a received email](/docs/api/reference/get-inbound-message) and [Get a received email's body](/docs/api/reference/get-inbound-message-body). Returns `404` when the message is unknown or its stored content has expired (received emails are retained for 30 days).