threadId. Papers groups incoming messages using their In-Reply-To and References headers within the same inbox. A matching subject alone does not join messages into a thread.
Filter the inbox message list to one conversation:
nextCursor to read additional pages. Fetch individual messages for their full content.
Use the reply endpoint to preserve the conversation. It sets reply headers when the parent’s email Message-ID is available. If that identifier has not arrived yet, Papers keeps its internal thread, but an external mail client may show a separate conversation.