Function extractThreadInfo

internal/relay/server.go:736–766

extractThreadInfo parses threading headers from a raw RFC 2822 message.

(body []byte)

// extractThreadInfo parses threading headers from a raw RFC 2822 message.
func extractThreadInfo(body []byte) threadInfo {
	msg, err := mail.ReadMessage(bytes.NewReader(body))
	if err != nil {
		return threadInfo{}
	}
	var refs []string
	if r := msg.Header.Get("References"); r != "" {
		for _, ref := range strings.Fields(r) {
			refs = append(refs, ref)
		}
	}
	// Extract From header email address
	fromHeader := ""
	if addr, err := mail.ParseAddress(msg.Header.Get("From")); err == nil {
		fromHeader = addr.Address
	}
	return threadInfo{
		MessageID:  msg.Header.Get("Message-Id"),
		Subject:    decodeMIMEHeader(msg.Header.Get("Subject")),
		InReplyTo:  msg.Header.Get("In-Reply-To"),
		References: refs,
		From:       fromHeader,
		// RFC 5322 § 3.6.2 allows multiple addresses in Reply-To. Mirror
		// the same parser used for To/Cc so display names get stripped
		// the same way and the field shape is uniform across consumers.
		ReplyTo:        extractAddressList(msg.Header.Get("Reply-To")),
		To:             extractAddressList(msg.Header.Get("To")),
		CC:             extractAddressList(msg.Header.Get("Cc")),
		ConversationID: msg.Header.Get("X-E2A-Conversation-Id"),
	}
}

// decodeMIMEHeader decodes any RFC 2047 encoded-word runs in a header value
// (e.g. `=?utf-8?Q?caf=C3=A9?=` → `café`). Used for display fields like