feat: name dragged/exported .eml files as "date (from-to) subject" with ASCII-only chars

components/email/email-viewer.tsx

@@ -3,6 +3,7 @@
 import { useState, useEffect, useLayoutEffect, useMemo, useRef, useCallback } from "react";
 import DOMPurify from "dompurify";
 import { Email, ContactCard, Mailbox } from "@/lib/jmap/types";
+import { emailExportFilename } from "@/lib/email-filename";
 import { EMAIL_IFRAME_SANITIZE_CONFIG, collapseBlockedImageContainers, escapeHtml, plainTextToSafeHtml, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
 import { hasMeaningfulHtmlBody } from "@/lib/signature-utils";
 import { Button } from "@/components/ui/button";
@@ -3056,8 +3057,7 @@ export function EmailViewer({
   const handleExportEmail = async () => {
     if (!email?.blobId || !client) return;
     try {
-      const subject = (email.subject || 'email').replace(/[<>:"/\\|?*]+/g, '_').slice(0, 100);
-      await client.downloadBlob(email.blobId, `${subject}.eml`, 'message/rfc822');
+      await client.downloadBlob(email.blobId, emailExportFilename(email), 'message/rfc822');
     } catch {
       toast.error(tNotifications('export_email_error'));
     }

hooks/use-email-drag.ts

@@ -1,4 +1,4 @@
-"use client";
+"use client";
 
 import { useCallback, useEffect, useRef, DragEvent } from "react";
 import { Email } from "@/lib/jmap/types";
@@ -8,6 +8,7 @@ import { useAuthStore } from "@/stores/auth-store";
 import { useDragDropContext } from "@/contexts/drag-drop-context";
 import { useUIStore } from "@/stores/ui-store";
 import { isDragOutSupported } from "@/hooks/use-attachment-drag";
+import { emailExportFilename } from "@/lib/email-filename";
 
 interface UseEmailDragOptions {
   email: Email;
@@ -48,36 +49,6 @@ function createDragPreview(count: number): HTMLElement {
   return preview;
 }
 
-function sanitizeFilenamePart(s: string, maxLen = 80): string {
-  // eslint-disable-next-line no-control-regex
-  const cleaned = s.replace(/[<>:"/\\|?*\x00-\x1F]+/g, "_").replace(/\s+/g, " ").trim();
-  return cleaned.slice(0, maxLen) || "";
-}
-
-function formatEmlDate(iso: string | null | undefined): string {
-  const d = iso ? new Date(iso) : new Date();
-  if (Number.isNaN(d.getTime())) return "0000-00-00 00.00.00";
-  const pad = (n: number) => String(n).padStart(2, "0");
-  return (
-    `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ` +
-    `${pad(d.getHours())}.${pad(d.getMinutes())}.${pad(d.getSeconds())}`
-  );
-}
-
-function addressLabel(addr: { name?: string | null; email: string } | undefined, maxLen = 30): string {
-  if (!addr) return "";
-  const label = (addr.name && addr.name.trim()) || addr.email.split("@")[0] || addr.email;
-  return sanitizeFilenamePart(label, maxLen);
-}
-
-function emlFilename(email: Email): string {
-  const date = formatEmlDate(email.receivedAt || email.sentAt);
-  const from = addressLabel(email.from?.[0]);
-  const to = addressLabel(email.to?.[0]);
-  const subject = sanitizeFilenamePart(email.subject || "no subject");
-  return `${date} (${from}-${to}) ${subject}.eml`;
-}
-
 function bundleFilename(count: number): string {
   return `emails-${count}.zip`;
 }
@@ -107,7 +78,7 @@ async function buildEmailZip(client: IJMAPClient, emails: Email[]): Promise<stri
   const used = new Set<string>();
   await Promise.all(
     eligible.map(async (em) => {
-      const base = emlFilename(em).replace(/\.eml$/, "");
+      const base = emailExportFilename(em).replace(/\.eml$/, "");
       let name = `${base}.eml`;
       while (used.has(name)) name = `${base} [${em.id.slice(0, 6)}].eml`;
       used.add(name);
@@ -179,7 +150,7 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
   const prefetchSingle = useCallback(() => {
     if (!dragOutEnabled || !client || !email.blobId) return;
     if (singleBlobUrlRef.current || inFlightRef.current) return;
-    const name = emlFilename(email);
+    const name = emailExportFilename(email);
     inFlightRef.current = client
       .fetchBlobAsObjectUrl(email.blobId, name, "message/rfc822")
       .then((url) => {
@@ -232,7 +203,7 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
       if (emailsToDrag.length === 1 && emailsToDrag[0].blobId) {
         const url = singleBlobUrlRef.current;
         if (url) {
-          const name = emlFilename(emailsToDrag[0]);
+          const name = emailExportFilename(emailsToDrag[0]);
           // `DownloadURL` format: <mime>:<filename>:<url>. Chromium reads this
           // on drop and writes a real file; Firefox/Safari ignore it.
           e.dataTransfer.setData(
@@ -240,7 +211,7 @@ export function useEmailDrag({ email, sourceMailboxId, threadEmails }: UseEmailD
             `message/rfc822:${encodeURIComponent(name)}:${url}`,
           );
         } else {
-          // Not warmed up yet — kick off so the next attempt works. Don't
+          // Not warmed up yet — kick off so the next attempt works. Don't
           // preventDefault: in-app drop still has to function.
           prefetchSingle();
         }

lib/email-filename.ts

@@ -0,0 +1,43 @@
+import type { Email } from "@/lib/jmap/types";
+
+// Restrict filenames to ASCII letters/digits and a small set of safe
+// punctuation. Everything else collapses to `_`. Keeps names predictable
+// across Windows/macOS/Linux file systems and avoids emoji/RTL/zero-width
+// surprises in subject lines.
+const SAFE_CHARS = /[^A-Za-z0-9 _\-().,!@#&+=[\]{}']/g;
+
+function sanitizePart(input: string, maxLen: number): string {
+  const cleaned = input
+    .replace(SAFE_CHARS, "_")
+    .replace(/_+/g, "_")
+    .replace(/\s+/g, " ")
+    .trim()
+    .replace(/^[._-]+|[._-]+$/g, "");
+  return cleaned.slice(0, maxLen);
+}
+
+function formatDate(iso: string | null | undefined): string {
+  const d = iso ? new Date(iso) : new Date();
+  if (Number.isNaN(d.getTime())) return "0000-00-00 00.00.00";
+  const pad = (n: number) => String(n).padStart(2, "0");
+  return (
+    `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ` +
+    `${pad(d.getHours())}.${pad(d.getMinutes())}.${pad(d.getSeconds())}`
+  );
+}
+
+function addressLabel(addr: { name?: string | null; email: string } | undefined, maxLen = 30): string {
+  if (!addr) return "unknown";
+  const raw = (addr.name && addr.name.trim()) || addr.email.split("@")[0] || addr.email;
+  return sanitizePart(raw, maxLen) || "unknown";
+}
+
+// Produce `YYYY-MM-DD HH.mm.SS (from-to) subject.eml`. All components are
+// sanitized to ASCII-safe filename characters.
+export function emailExportFilename(email: Email): string {
+  const date = formatDate(email.receivedAt || email.sentAt);
+  const from = addressLabel(email.from?.[0]);
+  const to = addressLabel(email.to?.[0]);
+  const subject = sanitizePart(email.subject || "no subject", 80) || "no subject";
+  return `${date} (${from}-${to}) ${subject}.eml`;
+}