Returns the parsed, decoded body of a received email as JSON: the `html` and `text` parts, each `null` when the message had no such part. This is the reading-friendly form; for the exact original bytes (headers, signatures, full MIME structure) use [Get a received email's raw content](/docs/api/reference/get-inbound-message-raw). An unknown or expired message returns `404`; a message that exists but has no stored content returns both parts `null`. The HTML body of the message, or null when the message had no HTML part. The plain-text body of the message, or null when the message had no text part.