Preserve QOutlook threading headers in EML

src/io/outlookMail.ts

@@ -90,6 +90,7 @@ export async function importEmlFile(file: File): Promise<ImportedMailMessage> {
     ...(parsed.headers.cc ? { cc: decodeMimeWords(parsed.headers.cc) } : {}),
     ...(parsed.headers.bcc ? { bcc: decodeMimeWords(parsed.headers.bcc) } : {}),
     ...(parsed.headers["reply-to"] ? { replyTo: decodeMimeWords(parsed.headers["reply-to"]) } : {}),
+    ...mailThreadHeaders(parsed.headers),
     subject: decodeMimeWords(parsed.headers.subject || "Без темы"),
     body: extractMessageBody(parsed.headers, parsed.body),
     time: parsed.headers.date || new Date().toLocaleString("ru-RU"),
@@ -127,6 +128,7 @@ export function msgDataToMailMessage(reader: Pick<MsgReaderInstance, "getAttachm
     ...(cc ? { cc } : {}),
     ...(bcc ? { bcc } : {}),
     ...(replyTo ? { replyTo } : {}),
+    ...mailThreadHeaders(headerFields),
     subject: firstText(data.subject, decodeMimeWords(headerFields.subject || ""), "Без темы"),
     body: msgBodyText(data),
     time: firstText(data.messageDeliveryTime, data.clientSubmitTime, data.creationTime, data.lastModificationTime, headerFields.date, new Date().toLocaleString("ru-RU")),
@@ -421,6 +423,7 @@ export function buildEmlSource(message: MailMessage): string {
       ...optionalAddressHeaders(message),
       `Subject: ${encodeHeaderValue(message.subject || "Без темы")}`,
       `Date: ${sanitizeHeaderValue(message.time || new Date().toUTCString())}`,
+      ...optionalThreadHeaders(message),
       "MIME-Version: 1.0",
       `Content-Type: multipart/mixed; boundary="${boundary}"`,
       "",
@@ -443,6 +446,7 @@ export function buildEmlSource(message: MailMessage): string {
     ...optionalAddressHeaders(message),
     `Subject: ${encodeHeaderValue(message.subject || "Без темы")}`,
     `Date: ${sanitizeHeaderValue(message.time || new Date().toUTCString())}`,
+    ...optionalThreadHeaders(message),
     "MIME-Version: 1.0",
     "Content-Type: text/plain; charset=utf-8",
     "Content-Transfer-Encoding: 8bit",
@@ -461,6 +465,26 @@ function optionalAddressHeaders(message: MailMessage): string[] {
   ];
 }
 
+function optionalThreadHeaders(message: MailMessage): string[] {
+  return [
+    ...(message.messageId?.trim() ? [`Message-ID: ${sanitizeHeaderValue(message.messageId)}`] : []),
+    ...(message.inReplyTo?.trim() ? [`In-Reply-To: ${sanitizeHeaderValue(message.inReplyTo)}`] : []),
+    ...(message.references?.trim() ? [`References: ${sanitizeHeaderValue(message.references)}`] : [])
+  ];
+}
+
+function mailThreadHeaders(headers: MailHeaders): Pick<MailMessage, "messageId" | "inReplyTo" | "references"> {
+  const messageId = sanitizeHeaderValue(headers["message-id"] || "");
+  const inReplyTo = sanitizeHeaderValue(headers["in-reply-to"] || "");
+  const references = sanitizeHeaderValue(headers.references || "");
+
+  return {
+    ...(messageId ? { messageId } : {}),
+    ...(inReplyTo ? { inReplyTo } : {}),
+    ...(references ? { references } : {})
+  };
+}
+
 export function decodeMimeWords(value: string): string {
   return value
     .replace(/(=\?[^?]+\?[bqBQ]\?[^?]+\?=)\s+(?==\?[^?]+\?[bqBQ]\?[^?]+\?=)/g, "$1")