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Yes, that's the In-Reply-To header. It contains the unique message identifier from the Message-ID field of the email you're replying to. See also https://tool
by alexjm 7y ago
Yes, that's the In-Reply-To header. It contains the unique message identifier from the Message-ID field of the email you're replying to.
See also https://tools.ietf.org/html/rfc822 https://tools.ietf.org/html/rfc822 sections 4.6.1 and 4.6.2
- leephillips 7y agoAnd that's what mature email clients use to present thread trees, to help make sense out of email conversations. Gmail, etc., are not mature email clients.
- JdeBP 7y agoObserve, furthermore, that References: was in part designed so that a MUA/NUA could reconstruct a tree even if some intermediate messages were missing.