feat: add "Forward as attachment" next to Export as .eml

Adds a "Forward as attachment" action to the message overflow menu
(desktop and mobile), right beside the existing "Export as .eml"
action. Opens a new forward-mode compose window with the original
message attached as a message/rfc822 file instead of quoted inline -
useful for reporting spam/phishing to an upstream gateway that expects
the raw original as an attachment (the primary motivating use case:
gateways like MxGuarddog require complete original headers, including
the full mail path, for scanning), or for preserving a message's exact
formatting/headers when forwarding.

Implementation reuses the composer's existing attachment-carry-forward
mechanism (the `attachments` useState initializer in
email-composer.tsx already carries a forwarded message's own
attachments into the new compose via `replyTo.attachments`) - this
just adds one synthetic entry representing the whole original message,
referenced by its existing blobId. No re-fetch or re-upload needed,
since JMAP blobs are account-scoped rather than per-email. The inline
quote-header step (prepareComposerQuoteHeader) is skipped, so the body
starts blank instead of quoting the original.

The core "build subject + attachment entry" logic is extracted into a
pure, unit-tested helper (lib/forward-as-attachment.ts) rather than
left inline in the already-large page component.

Adds the forward_as_attachment locale key to all 24 locales (English
text as a placeholder pending translation, following the existing
add-a-key convention) to satisfy the translations completeness test.

app/(main)/[locale]/page.tsx

@@ -77,6 +77,7 @@ import { appLifecycleHooks, uiHooks, routerHooks, toastHooks, emailHooks } from
 import { emailToReadView } from "@/lib/plugin-projection";
 import { buildQuoteHeader } from "@/lib/quote-header";
 import { buildReplySubject, buildForwardSubject } from "@/lib/subject-prefix";
+import { buildForwardAsAttachmentPayload } from "@/lib/forward-as-attachment";
 import { getEffectiveLocale } from '@/i18n/detect-locale';
 import type { QuoteHeader } from "@/lib/plugin-types";
 
@@ -1539,6 +1540,52 @@ export default function Home() {
     if (isMobile) setActiveView('viewer');
   };
 
+  // Forward the original message as a message/rfc822 attachment instead of
+  // inline-quoted text - e.g. for reporting spam to an upstream gateway
+  // that expects the raw original as an attachment, or preserving exact
+  // formatting/headers the recipient needs to see untouched. Reuses the
+  // same attachment-carry-forward mechanism native Forward already uses
+  // for a forwarded message's own attachments (see the `attachments`
+  // useState initializer in email-composer.tsx) - we just add one more
+  // synthetic entry representing the whole original message, referenced
+  // by its existing blobId (no re-fetch/re-upload needed - JMAP blobs are
+  // account-scoped, not per-email). Skips prepareComposerQuoteHeader
+  // entirely, so the body starts blank instead of quoting the original.
+  const handleForwardAsAttachment = async () => {
+    if (!selectedEmail) return;
+    const payload = buildForwardAsAttachmentPayload(selectedEmail, t('email_composer.prefix.forward'));
+    if (!payload) return;
+
+    const ok = await emailHooks.onBeforeForward.intercept({
+      originalEmailId: selectedEmail.id,
+      originalEmail: emailToReadView(selectedEmail),
+      mode: 'forward' as const,
+    });
+    if (!ok) return;
+
+    startFreshComposerSession();
+    setPendingDraft({
+      to: "",
+      cc: "",
+      bcc: "",
+      subject: payload.subject,
+      body: "",
+      showCc: false,
+      showBcc: false,
+      selectedIdentityId: null,
+      subAddressTag: "",
+      mode: "forward",
+      draftId: null,
+      replyTo: {
+        subject: selectedEmail.subject,
+        attachments: [payload.attachment],
+      },
+    });
+    setComposerMode('forward');
+    setShowComposer(true);
+    if (isMobile) setActiveView('viewer');
+  };
+
   const handleDelete = async (emailToDelete: Email | null = selectedEmail) => {
     if (!client || !emailToDelete) return;
 
@@ -3436,6 +3483,7 @@ export default function Home() {
                     onReply={handleReply}
                     onReplyAll={handleReplyAll}
                     onForward={handleForward}
+                    onForwardAsAttachment={handleForwardAsAttachment}
                     onDelete={() => {
                       // Deleting the open message returns to the list (Gmail-style),
                       // not the next email — unless the user turned the setting off.

components/email/email-viewer.tsx

@@ -19,6 +19,7 @@ import {
   Reply,
   ReplyAll,
   Forward,
+  Paperclip,
   Trash2,
   Archive,
   Star,
@@ -109,6 +110,7 @@ interface EmailViewerProps {
   onReply?: (draftText?: string) => void;
   onReplyAll?: () => void;
   onForward?: () => void;
+  onForwardAsAttachment?: () => void;
   onDelete?: () => void;
   onArchive?: () => void;
   onToggleStar?: () => void;
@@ -621,6 +623,7 @@ export function EmailViewer({
   onReply,
   onReplyAll,
   onForward,
+  onForwardAsAttachment,
   onDelete,
   onArchive,
   onToggleStar,
@@ -3340,6 +3343,16 @@ export function EmailViewer({
                 </button>
               )}
               <div className="h-px bg-border my-1" />
+              {/* Forward as attachment */}
+              {onForwardAsAttachment && (
+                <button
+                  onClick={() => { onForwardAsAttachment(); setMoreMenuOpen(false); setMoreMenuSub(null); }}
+                  className="w-full px-3 py-1.5 text-sm text-start hover:bg-muted text-foreground flex items-center gap-2"
+                >
+                  <Paperclip className="w-4 h-4" />
+                  {t('forward_as_attachment')}
+                </button>
+              )}
               {/* Export email */}
               <button
                 onClick={() => { handleExportEmail(); setMoreMenuOpen(false); setMoreMenuSub(null); }}
@@ -3462,6 +3475,15 @@ export function EmailViewer({
                 </button>
               )}
               <div className="h-px bg-border my-1" />
+              {onForwardAsAttachment && (
+                <button
+                  onClick={() => { onForwardAsAttachment(); setMoreMenuOpen(false); }}
+                  className="w-full px-4 py-3 min-h-[44px] text-sm text-start hover:bg-muted text-foreground flex items-center gap-3"
+                >
+                  <Paperclip className="w-5 h-5" />
+                  {t('forward_as_attachment')}
+                </button>
+              )}
               <button
                 onClick={() => { handleExportEmail(); setMoreMenuOpen(false); }}
                 className="w-full px-4 py-3 min-h-[44px] text-sm text-start hover:bg-muted text-foreground flex items-center gap-3"

lib/__tests__/forward-as-attachment.test.ts

@@ -0,0 +1,48 @@
+import { describe, it, expect } from 'vitest';
+import { buildForwardAsAttachmentPayload } from '@/lib/forward-as-attachment';
+import type { Email } from '@/lib/jmap/types';
+
+function makeEmail(overrides: Partial<Email> = {}): Email {
+  return {
+    id: 'e1',
+    threadId: 't1',
+    mailboxIds: { inbox: true },
+    keywords: {},
+    size: 12345,
+    receivedAt: '2026-07-26T22:25:22Z',
+    subject: 'Your waste service day is changing',
+    hasAttachment: false,
+    blobId: 'blob123',
+    ...overrides,
+  };
+}
+
+describe('buildForwardAsAttachmentPayload', () => {
+  it('returns null when the email has no blobId', () => {
+    const email = makeEmail({ blobId: undefined });
+    expect(buildForwardAsAttachmentPayload(email, 'Fwd:')).toBeNull();
+  });
+
+  it('prefixes the subject using the given forward prefix', () => {
+    const email = makeEmail({ subject: 'Missed spam example' });
+    const payload = buildForwardAsAttachmentPayload(email, 'Fwd:');
+    expect(payload?.subject).toBe('Fwd: Missed spam example');
+  });
+
+  it('builds a message/rfc822 attachment referencing the email\'s own blobId, not a new upload', () => {
+    const email = makeEmail({ blobId: 'the-real-blob-id', size: 26489 });
+    const payload = buildForwardAsAttachmentPayload(email, 'Fwd:');
+    expect(payload?.attachment).toEqual({
+      blobId: 'the-real-blob-id',
+      name: expect.stringMatching(/\.eml$/),
+      type: 'message/rfc822',
+      size: 26489,
+    });
+  });
+
+  it('is idempotent - repeated forwarding does not stack prefixes', () => {
+    const email = makeEmail({ subject: 'Fwd: already forwarded once' });
+    const payload = buildForwardAsAttachmentPayload(email, 'Fwd:');
+    expect(payload?.subject).toBe('Fwd: already forwarded once');
+  });
+});

lib/forward-as-attachment.ts

@@ -0,0 +1,44 @@
+import type { Email } from "@/lib/jmap/types";
+import { buildForwardSubject } from "@/lib/subject-prefix";
+import { emailExportFilename } from "@/lib/download-filename";
+
+export interface ForwardAsAttachmentEntry {
+  blobId: string;
+  name: string;
+  type: "message/rfc822";
+  size: number;
+}
+
+export interface ForwardAsAttachmentPayload {
+  subject: string;
+  attachment: ForwardAsAttachmentEntry;
+}
+
+/**
+ * Build the subject and synthetic attachment entry for forwarding a
+ * message as a message/rfc822 attachment instead of inline-quoted text
+ * (e.g. reporting spam to an upstream gateway that expects the raw
+ * original as an attachment, or preserving exact formatting/headers).
+ *
+ * Referenced by blobId, not re-uploaded - JMAP blobs are account-scoped,
+ * not per-email, so the same blobId a message already has can be attached
+ * to a brand new outgoing email directly.
+ *
+ * Returns null when the email has no blobId (nothing to reference).
+ */
+export function buildForwardAsAttachmentPayload(
+  email: Email,
+  forwardPrefix: string,
+): ForwardAsAttachmentPayload | null {
+  if (!email.blobId) return null;
+
+  return {
+    subject: buildForwardSubject(email.subject, forwardPrefix),
+    attachment: {
+      blobId: email.blobId,
+      name: emailExportFilename(email),
+      type: "message/rfc822",
+      size: email.size,
+    },
+  };
+}

locales/ar/common.json

@@ -298,6 +298,7 @@
     "print": "طباعة",
     "view_source": "عرض المصدر",
     "export_email": "تصدير كملف ‎.eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "استيراد ملف ‎.eml أو ‎.zip",
     "keyboard_shortcuts": "اختصارات لوحة المفاتيح (؟)",
     "email_source": "مصدر الرسالة",

locales/ca/common.json

@@ -298,6 +298,7 @@
     "print": "Imprimeix",
     "view_source": "Mostra el codi font",
     "export_email": "Exporta com a .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importa .eml o .zip",
     "keyboard_shortcuts": "Dreceres de teclat (?)",
     "email_source": "Codi font del correu",

locales/cs/common.json

@@ -298,6 +298,7 @@
     "print": "Tisk",
     "view_source": "Zobrazit zdrojový kód",
     "export_email": "Exportovat jako .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importovat .eml nebo .zip",
     "keyboard_shortcuts": "Klávesové zkratky (?)",
     "email_source": "Zdrojový kód zprávy",

locales/da/common.json

@@ -298,6 +298,7 @@
     "print": "Udskriv",
     "view_source": "Vis kilde",
     "export_email": "Eksportér som .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importér .eml eller .zip",
     "keyboard_shortcuts": "Tastaturgenveje (?)",
     "email_source": "E-mail-kilde",

locales/de/common.json

@@ -298,6 +298,7 @@
     "print": "Drucken",
     "view_source": "Quelltext anzeigen",
     "export_email": "Als .eml exportieren",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": ".eml oder .zip importieren",
     "keyboard_shortcuts": "Tastaturkürzel (?)",
     "email_source": "E-Mail-Quelltext",

locales/en/common.json

@@ -298,6 +298,7 @@
     "print": "Print",
     "view_source": "View source",
     "export_email": "Export as .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Import .eml or .zip",
     "keyboard_shortcuts": "Keyboard shortcuts (?)",
     "email_source": "Email Source",

locales/es/common.json

@@ -298,6 +298,7 @@
     "print": "Imprimir",
     "view_source": "Ver código fuente",
     "export_email": "Exportar como .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importar .eml o .zip",
     "keyboard_shortcuts": "Atajos de teclado (?)",
     "email_source": "Código Fuente del Correo",

locales/fa/common.json

@@ -298,6 +298,7 @@
     "print": "چاپ",
     "view_source": "مشاهده منبع",
     "export_email": "خروجی .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "وارد کردن .eml یا .zip",
     "keyboard_shortcuts": "میانبرهای صفحه کلید (?)",
     "email_source": "منبع ایمیل",

locales/fr/common.json

@@ -298,6 +298,7 @@
     "print": "Imprimer",
     "view_source": "Voir la source",
     "export_email": "Exporter en .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importer .eml ou .zip",
     "keyboard_shortcuts": "Raccourcis clavier (?)",
     "email_source": "Source de l'email",

locales/he/common.json

@@ -245,6 +245,7 @@
     "print": "הדפס",
     "view_source": "צפה במקור",
     "export_email": "ייצא כ-.eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "ייבוא .eml",
     "keyboard_shortcuts": "קיצורי מקשים (?)",
     "email_source": "מקור דוא\"ל",

locales/hu/common.json

@@ -298,6 +298,7 @@
     "print": "Nyomtatás",
     "view_source": "Forrás megtekintése",
     "export_email": "Exportálás .eml-ként",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importálás .eml vagy .zip fájlból",
     "keyboard_shortcuts": "Billentyűparancsok (?)",
     "email_source": "E-mail forrás",

locales/it/common.json

@@ -298,6 +298,7 @@
     "print": "Stampa",
     "view_source": "Visualizza sorgente",
     "export_email": "Esporta come .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importa .eml o .zip",
     "keyboard_shortcuts": "Scorciatoie da tastiera (?)",
     "email_source": "Sorgente del messaggio",

locales/ja/common.json

@@ -298,6 +298,7 @@
     "print": "印刷",
     "view_source": "ソースを表示",
     "export_email": ".emlとしてエクスポート",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": ".eml または .zip をインポート",
     "keyboard_shortcuts": "キーボードショートカット (?)",
     "email_source": "メールソース",

locales/ko/common.json

@@ -298,6 +298,7 @@
     "print": "인쇄",
     "view_source": "원본 보기",
     "export_email": ".eml 파일로 내보내기",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": ".eml 또는 .zip 가져오기",
     "keyboard_shortcuts": "단축키 (?)",
     "email_source": "메일 원본",

locales/lv/common.json

@@ -298,6 +298,7 @@
     "print": "Drukāt",
     "view_source": "Skatīt avota kodu",
     "export_email": "Eksportēt kā .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importēt .eml vai .zip",
     "keyboard_shortcuts": "Īsinājumtaustiņi (?)",
     "email_source": "Vēstules avota kods",

locales/nl/common.json

@@ -298,6 +298,7 @@
     "print": "Afdrukken",
     "view_source": "Bron bekijken",
     "export_email": "Exporteren als .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": ".eml of .zip importeren",
     "keyboard_shortcuts": "Sneltoetsen (?)",
     "email_source": "E-mailbron",

locales/pl/common.json

@@ -298,6 +298,7 @@
     "print": "Drukuj",
     "view_source": "Pokaż źródło",
     "export_email": "Eksportuj jako .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importuj .eml lub .zip",
     "keyboard_shortcuts": "Skróty klawiszowe (?)",
     "email_source": "Źródło wiadomości",

locales/pt/common.json

@@ -298,6 +298,7 @@
     "print": "Imprimir",
     "view_source": "Ver código-fonte",
     "export_email": "Exportar como .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importar .eml ou .zip",
     "keyboard_shortcuts": "Atalhos de teclado (?)",
     "email_source": "Código-fonte do E-mail",

locales/ro/common.json

@@ -298,6 +298,7 @@
     "print": "Imprimare",
     "view_source": "Vizualizați sursa",
     "export_email": "Exportați ca fișier .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importați fișiere .eml sau .zip",
     "keyboard_shortcuts": "Comenzi rapide de la tastatură (?)",
     "email_source": "Sursa e-mailului",

locales/ru/common.json

@@ -298,6 +298,7 @@
     "print": "Распечатать",
     "view_source": "Просмотреть исходный код",
     "export_email": "Экспортировать как .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Импортировать .eml или .zip",
     "keyboard_shortcuts": "Сочетания клавиш (?)",
     "email_source": "Исходный код письма",

locales/sk/common.json

@@ -298,6 +298,7 @@
     "print": "Tlačiť",
     "view_source": "Zobraziť zdrojový kód",
     "export_email": "Exportovať ako .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Importovať .eml alebo .zip",
     "keyboard_shortcuts": "Klávesové skratky (?)",
     "email_source": "Zdrojový kód e-mailu",

locales/tr/common.json

@@ -298,6 +298,7 @@
     "print": "Yazdır",
     "view_source": "Kaynağı görüntüle",
     "export_email": ".eml olarak dışa aktar",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": ".eml veya .zip içe aktar",
     "keyboard_shortcuts": "Klavye kısayolları (?)",
     "email_source": "E-posta Kaynağı",

locales/uk/common.json

@@ -298,6 +298,7 @@
     "print": "Роздрукувати",
     "view_source": "Переглянути джерело",
     "export_email": "Експортувати як .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "Імпорт .eml або .zip",
     "keyboard_shortcuts": "Комбінації клавіш (?)",
     "email_source": "Джерело електронної пошти",

locales/zh/common.json

@@ -298,6 +298,7 @@
     "print": "打印",
     "view_source": "查看源码",
     "export_email": "导出为 .eml",
+    "forward_as_attachment": "Forward as attachment",
     "import_email": "导入 .eml 或 .zip",
     "keyboard_shortcuts": "键盘快捷键（？）",
     "email_source": "邮件源码",