Threading

When a message arrives (inbound or outbound), Robotomail resolves its thread using two strategies in order:

1. Header matching: If the message has an In-Reply-To or References header, Robotomail looks up the referenced message ID and joins that thread.
2. Subject fallback: If no header match is found, Robotomail normalizes the subject (strips Re:, Fwd:, whitespace) and matches against existing threads in the same mailbox.

If neither strategy matches, a new thread is created.

To reply to a message, pass the original message's messageId (the RFC 5322 Message-ID, not the Robotomail UUID) in the inReplyTo field when sending. Robotomail automatically sets the In-Reply-To and References headers and joins the existing thread.

List threads via GET /v1/mailboxes/:id/threads and fetch a thread with all its messages via GET /v1/mailboxes/:id/threads/:threadId. See the Threads API reference.