Offline compose: write mail offline, Scheduled folder, undo countdown fix

Compose, Reply and Forward work offline. Drafts are kept on the device
(IndexedDB, lib/scheduled.ts), with files attached offline; Send becomes
"Schedule" and puts the message in a new Scheduled folder. When the server
is reachable again, scheduled messages are sent through the normal outbox
(Undo offered for a single one) and offline drafts become server drafts —
files uploaded first, each step recorded so nothing is created or sent
twice, under a Web Lock so two tabs never send the same message. Drafts
written offline show in Drafts as "On this device". Sign-out sends what
is scheduled, then wipes the device's copy.

Also: offline failures from keyboard shortcuts show "Not available
offline"; no recipient suggestions are asked for offline; a reply no
longer quotes an error page when the original is not saved.

The undo countdown counted to the server's deadline on the browser's
clock, so a few seconds of skew showed (18 s instead of 10). /send now
also returns undo_seconds, and the composer counts down from that.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/api/compose.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 import uuid
-from datetime import timedelta
+from datetime import UTC, datetime, timedelta
 from typing import Annotated
 
 from fastapi import APIRouter, Depends, File, Query, UploadFile
@@ -300,7 +300,10 @@ async def send(body: SendRequest, user: CurrentUser, db: DbSession) -> SendRespo
         str(outbox.id),
         _defer_by=timedelta(seconds=get_settings().undo_seconds),
     )
-    return SendResponse(outbox_id=outbox.id, undo_until=outbox.send_after.isoformat())
+    left = max(0.0, (outbox.send_after - datetime.now(UTC)).total_seconds())
+    return SendResponse(
+        outbox_id=outbox.id, undo_until=outbox.send_after.isoformat(), undo_seconds=left
+    )
 
 
 @router.post("/send/{outbox_id}/undo")

backend/app/outbox/schemas.py

@@ -56,6 +56,9 @@ class SendRequest(BaseModel):
 class SendResponse(BaseModel):
     outbox_id: uuid.UUID
     undo_until: str
+    # The same deadline as seconds from now: the browser counts down from this,
+    # since its clock may be seconds off the server's.
+    undo_seconds: float
 
 
 class OutboxStateOut(BaseModel):

backend/tests/outbox/test_outbox.py

@@ -398,6 +398,8 @@ async def test_send_creates_outbox_and_defers(ctx: Ctx) -> None:
     resp = await ctx.client.post("/api/send", json={"draft_id": did}, headers=_hdr())
     assert resp.status_code == 200
     outbox_id = resp.json()["outbox_id"]
+    # The window as a duration too, so the browser's clock does not matter.
+    assert 0 < resp.json()["undo_seconds"] <= get_settings().undo_seconds
 
     ob = await ctx.session.get(Outbox, uuid.UUID(outbox_id))
     assert ob is not None and ob.state == "undo_window"

frontend/src/components/Offline.tsx

@@ -5,10 +5,11 @@
 //  - OfflineIndicator (the sidebar header): the amber "Offline" cloud, with an
 //    explanation on click, and a short green "Back online" when it returns.
 
-import { useQueryClient } from "@tanstack/react-query";
-import { useEffect, useRef, useState, useSyncExternalStore } from "react";
+import { type QueryClient, useQueryClient } from "@tanstack/react-query";
+import { useEffect, useRef, useState } from "react";
 
 import { useT } from "../i18n";
+import { isOfflineError } from "../lib/api";
 import {
   isOffline,
   offlineEnabled,
@@ -19,40 +20,22 @@ import {
   useOffline,
   useOfflineEnabled,
 } from "../lib/offline";
+import {
+  clearOfflineNotice,
+  setBackOnline,
+  showOfflineNotice,
+  useBackOnline,
+  useOfflineNotice,
+} from "../lib/offlineNotice";
 import { prefetchRecent, serverAnswers } from "../lib/offlinePrefetch";
+import { flushLocal, type ScheduledSent } from "../lib/scheduled";
 import { subscribeWs } from "../lib/ws";
+import { hasUndoHost, offerUndo } from "./compose/undoSend";
 
 const PROBE_MS = 10_000;
 const BACK_ONLINE_MS = 3_000;
 const REFRESH_MS = 15 * 60_000;
 
-// ---- the short-lived bits of UI the two share ---------------------------------
-
-type Notice = { key: "offline" | "offlineNotSaved" | "notAvailable"; seq: number } | null;
-
-let notice: Notice = null;
-let backOnline = false;
-const listeners = new Set<() => void>();
-const emit = () => listeners.forEach((l) => l());
-const subscribe = (l: () => void) => {
-  listeners.add(l);
-  return () => {
-    listeners.delete(l);
-  };
-};
-let noticeTimer: number | undefined;
-let noticeSeq = 0;
-
-function showNotice(key: NonNullable<Notice>["key"], ms: number) {
-  notice = { key, seq: ++noticeSeq };
-  emit();
-  window.clearTimeout(noticeTimer);
-  noticeTimer = window.setTimeout(() => {
-    notice = null;
-    emit();
-  }, ms);
-}
-
 function CloudOff({ size = 16 }: { size?: number }) {
   return (
     <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.9" strokeLinecap="round" strokeLinejoin="round" aria-hidden>
@@ -63,6 +46,15 @@ function CloudOff({ size = 16 }: { size?: number }) {
   );
 }
 
+export function Clock({ size = 16 }: { size?: number }) {
+  return (
+    <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.9" strokeLinecap="round" strokeLinejoin="round" aria-hidden>
+      <circle cx="12" cy="12" r="8.5" />
+      <path d="M12 7.5V12l3 2" />
+    </svg>
+  );
+}
+
 function Check({ size = 16 }: { size?: number }) {
   return (
     <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.2" strokeLinecap="round" strokeLinejoin="round" aria-hidden>
@@ -73,12 +65,33 @@ function Check({ size = 16 }: { size?: number }) {
 
 // ---- the controller ------------------------------------------------------------
 
+/** Hand messages written offline to the server; offer Undo for a single send. */
+async function sendScheduled(queryClient: QueryClient): Promise<void> {
+  if (isOffline()) return;
+  let sent: ScheduledSent[];
+  try {
+    sent = await flushLocal();
+  } catch {
+    return;
+  }
+  for (const key of ["drafts", "drafts-remote", "folder-counts", "threads"]) {
+    void queryClient.invalidateQueries({ queryKey: [key] });
+  }
+  if (!sent.length) return;
+  if (sent.length === 1 && hasUndoHost()) {
+    const [one] = sent;
+    offerUndo({ outboxId: one.outboxId, draftId: one.draftId, until: Date.now() + one.undoSeconds * 1000 });
+  } else {
+    showOfflineNotice("sendingScheduled", 6000, { count: sent.length });
+  }
+}
+
 export function OfflineController() {
   const t = useT();
   const queryClient = useQueryClient();
   const offline = useOffline();
   const enabled = useOfflineEnabled();
-  const current = useSyncExternalStore(subscribe, () => notice);
+  const current = useOfflineNotice();
   const wasOffline = useRef(false);
 
   // Install (or remove) the service worker to match this device's setting.
@@ -90,23 +103,35 @@ export function OfflineController() {
   useEffect(() => {
     if (offline) {
       wasOffline.current = true;
-      showNotice(offlineEnabled() ? "offline" : "offlineNotSaved", 6000);
+      showOfflineNotice(offlineEnabled() ? "offline" : "offlineNotSaved", 6000);
       return;
     }
     if (!wasOffline.current) return;
     wasOffline.current = false;
-    notice = null;
-    backOnline = true;
-    emit();
-    const timer = window.setTimeout(() => {
-      backOnline = false;
-      emit();
-    }, BACK_ONLINE_MS);
+    clearOfflineNotice();
+    setBackOnline(true);
+    const timer = window.setTimeout(() => setBackOnline(false), BACK_ONLINE_MS);
     void queryClient.invalidateQueries();
+    void sendScheduled(queryClient);
     void prefetchRecent();
     return () => window.clearTimeout(timer);
   }, [offline, queryClient]);
 
+  // Messages written offline: sent (Scheduled) or made server drafts as soon
+  // as the server is there — on start, and checked again every minute.
+  useEffect(() => {
+    const start = window.setTimeout(() => void sendScheduled(queryClient), 2000);
+    const every = window.setInterval(() => void sendScheduled(queryClient), 60_000);
+    // A scheduled message was looked at and closed: no need to wait a minute.
+    const now = () => void sendScheduled(queryClient);
+    window.addEventListener("webmail:send-scheduled", now);
+    return () => {
+      window.clearTimeout(start);
+      window.clearInterval(every);
+      window.removeEventListener("webmail:send-scheduled", now);
+    };
+  }, [queryClient]);
+
   // While offline: ask the server now and then whether it is back.
   useEffect(() => {
     if (!offline) return;
@@ -151,10 +176,21 @@ export function OfflineController() {
       if (!el) return;
       e.preventDefault();
       e.stopPropagation();
-      showNotice("notAvailable", 2500);
+      showOfflineNotice("notAvailable", 2500);
+    };
+    // Actions started some other way (a keyboard shortcut, say) fail with
+    // "offline" somewhere unhandled: say so the same way, not as a page error.
+    const onRejection = (e: PromiseRejectionEvent) => {
+      if (!isOfflineError(e.reason)) return;
+      e.preventDefault();
+      showOfflineNotice("notAvailable", 2500);
     };
     document.addEventListener("click", onClick, true);
-    return () => document.removeEventListener("click", onClick, true);
+    window.addEventListener("unhandledrejection", onRejection);
+    return () => {
+      document.removeEventListener("click", onClick, true);
+      window.removeEventListener("unhandledrejection", onRejection);
+    };
   }, []);
 
   if (!current) return null;
@@ -164,14 +200,24 @@ export function OfflineController() {
       role="status"
       className="wm-offline-notice pointer-events-none fixed bottom-6 left-1/2 z-[70] flex max-w-[calc(100vw-2rem)] -translate-x-1/2 items-center gap-2.5 rounded-xl border border-app-border bg-app-elevated px-4 py-2.5 text-sm text-app-fg shadow-lg"
     >
-      <span className="text-amber-500">
-        <CloudOff size={18} />
-      </span>
+      {current.key === "scheduled" || current.key === "sendingScheduled" ? (
+        <span className="text-app-accent">
+          <Clock size={18} />
+        </span>
+      ) : (
+        <span className="text-amber-500">
+          <CloudOff size={18} />
+        </span>
+      )}
       {current.key === "offline"
         ? t("offline.noticeSaved")
         : current.key === "offlineNotSaved"
           ? t("offline.noticeNotSaved")
-          : t("offline.notAvailable")}
+          : current.key === "scheduled"
+            ? t("offline.noticeScheduled")
+            : current.key === "sendingScheduled"
+              ? t("offline.noticeSendingScheduled", current.vars)
+              : t("offline.notAvailable")}
     </div>
   );
 }
@@ -182,7 +228,7 @@ export function OfflineIndicator({ compact = false }: { compact?: boolean }) {
   const t = useT();
   const offline = useOffline();
   const enabled = useOfflineEnabled();
-  const back = useSyncExternalStore(subscribe, () => backOnline);
+  const back = useBackOnline();
   const last = useLastSync();
   const when = savedWhen(last);
   const [open, setOpen] = useState(false);

frontend/src/components/compose/Composer.tsx

@@ -2,8 +2,22 @@ import { useQuery } from "@tanstack/react-query";
 import { useEffect, useRef, useState } from "react";
 
 import { useT } from "../../i18n";
-import { api, ApiError } from "../../lib/api";
+import { api, ApiError, isOfflineError } from "../../lib/api";
+import { isOffline, useOffline } from "../../lib/offline";
+import {
+  deleteFiles,
+  deleteLocal,
+  holdOpen,
+  type LocalFile,
+  type LocalMessage,
+  type LocalState,
+  newLocalId,
+  putFile,
+  putLocal,
+  uploadFiles,
+} from "../../lib/scheduled";
 import type { AccountOut, AttachmentOut, DraftInput, DraftOut } from "../../lib/types";
+import { showOfflineNotice } from "../../lib/offlineNotice";
 import { RecipientChips } from "./RecipientChips";
 import { RichTextEditor, type RichTextEditorHandle } from "./RichTextEditor";
 import { hasUndoHost, offerUndo } from "./undoSend";
@@ -17,6 +31,7 @@ export interface ComposerInit {
   kind: string; // reply | reply_all | forward | new
   to?: string;
   cc?: string;
+  bcc?: string;
   subject?: string;
   text?: string;
   html?: string; // initial body when reopening an existing draft
@@ -25,6 +40,11 @@ export interface ComposerInit {
   // A reply/forward quotes the original: this attribution line sits above the
   // quoted message body (fetched from the original message's sanitized HTML).
   quote?: { attribution: string; messageId: string };
+  // A message kept on this device (written offline; lib/scheduled.ts).
+  localId?: string;
+  localState?: LocalState; // "scheduled" when reopened from Scheduled
+  attachments?: AttachmentOut[]; // known already: no need to ask the server
+  localFiles?: LocalFile[];
 }
 
 // Build the composer seed from a saved draft (used to reopen it in place or in a
@@ -45,6 +65,29 @@ export function draftToInit(draft: DraftOut): ComposerInit {
   };
 }
 
+// Reopen a message kept on this device (a draft written offline, or one in
+// Scheduled).
+export function localToInit(msg: LocalMessage): ComposerInit {
+  const p = msg.input.payload;
+  return {
+    accountId: msg.input.account_id,
+    threadId: msg.input.thread_id ?? null,
+    replyToMessageId: msg.input.reply_to_message_id ?? null,
+    kind: msg.input.kind,
+    to: p.to.join(", "),
+    cc: p.cc.join(", "),
+    bcc: p.bcc.join(", "),
+    subject: p.subject,
+    text: p.text,
+    html: p.html || undefined,
+    draftId: msg.serverDraftId ?? undefined,
+    localId: msg.id,
+    localState: msg.state === "draft" ? "draft" : "scheduled", // "failed"/"sending" wait to be sent too
+    attachments: msg.attachments,
+    localFiles: msg.files,
+  };
+}
+
 function splitList(value: string): string[] {
   return value
     .split(",")
@@ -80,11 +123,13 @@ function HeaderButton({
   onClick,
   title,
   active = false,
+  className = "",
   children,
 }: {
   onClick?: () => void;
   title: string;
   active?: boolean;
+  className?: string;
   children: React.ReactNode;
 }) {
   return (
@@ -93,7 +138,7 @@ function HeaderButton({
       title={title}
       aria-label={title}
       onClick={onClick}
-      className={`flex items-center gap-1 rounded-md px-2 py-1.5 text-sm ${
+      className={`${className} flex items-center gap-1 rounded-md px-2 py-1.5 text-sm ${
         active ? "bg-app-active text-app-fg" : "text-app-muted hover:bg-app-hover hover:text-app-fg"
       }`}
     >
@@ -150,8 +195,8 @@ export function Composer({
   const [accountId, setAccountId] = useState(init.accountId);
   const [to, setTo] = useState(init.to ?? "");
   const [cc, setCc] = useState(init.cc ?? "");
-  const [bcc, setBcc] = useState("");
-  const [showCc, setShowCc] = useState(Boolean(init.cc));
+  const [bcc, setBcc] = useState(init.bcc ?? "");
+  const [showCc, setShowCc] = useState(Boolean(init.cc || init.bcc));
   const [subject, setSubject] = useState(init.subject ?? "");
   const [bodyHtml, setBodyHtml] = useState(init.html ?? "");
   const [quoteHtml, setQuoteHtml] = useState("");
@@ -176,9 +221,12 @@ export function Composer({
   });
   const moreRef = useRef<HTMLDivElement>(null);
   const fromRef = useRef<HTMLDivElement>(null);
-  const [attachments, setAttachments] = useState<AttachmentOut[]>([]);
+  const [attachments, setAttachments] = useState<AttachmentOut[]>(init.attachments ?? []);
+  // Files attached while offline, kept on this device until they can be uploaded.
+  const [localFiles, setLocalFiles] = useState<LocalFile[]>(init.localFiles ?? []);
   const [attachError, setAttachError] = useState("");
-  const [status, setStatus] = useState<"" | "saving" | "saved" | "sending" | "error">("");
+  const [status, setStatus] = useState<"" | "saving" | "saved" | "savedLocal" | "sending" | "error">("");
+  const offline = useOffline();
   const [undo, setUndo] = useState<{ outboxId: string; until: number } | null>(null);
   const [undoLeft, setUndoLeft] = useState(0);
   // Tick the undo countdown while the window is open.
@@ -199,6 +247,11 @@ export function Composer({
     onTitleRef.current?.(subject);
   }, [subject]);
   const draftId = useRef<string | null>(init.draftId ?? null);
+  // This message's copy on this device, while there is one (lib/scheduled.ts).
+  const localId = useRef<string | null>(init.localId ?? null);
+  const discardedRef = useRef(false);
+  // Kept as what it was opened as: a scheduled message edited offline stays scheduled.
+  const localState = useRef<LocalState>(init.localState ?? "draft");
   const sentRef = useRef(false); // send initiated -> don't mirror to Drafts on close
   // Whether the user actually edited anything. Merely opening a draft to view it
   // must not re-save/re-mirror it (that spawned duplicate IMAP copies).
@@ -249,6 +302,8 @@ export function Composer({
     (async () => {
       try {
         const resp = await fetch(api.messageHtmlUrl(quote.messageId), { credentials: "include" });
+        // Offline, a message not saved here answers 503: quote nothing rather than that.
+        if (!resp.ok) throw new Error(`quote: ${resp.status}`);
         const doc = new DOMParser().parseFromString(await resp.text(), "text/html");
         if (!cancelled) setQuoteHtml(doc.body?.innerHTML ?? "");
       } catch {
@@ -265,7 +320,7 @@ export function Composer({
   // Resolve attachment metadata when reopening a draft that already has some.
   useEffect(() => {
     const ids = init.attachmentIds ?? [];
-    if (ids.length === 0) return;
+    if (ids.length === 0 || init.attachments) return;
     let cancelled = false;
     (async () => {
       try {
@@ -290,6 +345,12 @@ export function Composer({
         continue;
       }
       try {
+        if (isOffline()) {
+          // Kept on this device, uploaded once the server is reachable.
+          const kept = await putFile(file);
+          setLocalFiles((prev) => [...prev, kept]);
+          continue;
+        }
         const att = await api.uploadComposeAttachment(file);
         setAttachments((prev) => [...prev, att]);
       } catch (e) {
@@ -303,6 +364,12 @@ export function Composer({
     setAttachments((prev) => prev.filter((a) => a.id !== id));
   };
 
+  const removeLocalFile = (id: string) => {
+    markDirty();
+    setLocalFiles((prev) => prev.filter((f) => f.id !== id));
+    void deleteFiles([id]);
+  };
+
   // Drag & drop: files dropped on the writing area insert inline (images) or
   // attach (other types); dropped anywhere above it, everything attaches.
   const editorAreaRef = useRef<HTMLDivElement>(null);
@@ -393,7 +460,7 @@ export function Composer({
 
   const bodyReady = quoteResolved && accountsQuery.data !== undefined;
 
-  const payload = (): DraftInput => {
+  const payload = (atts: AttachmentOut[] = attachments): DraftInput => {
     const html = bodyHtml || initialHtml;
     return {
       account_id: accountId,
@@ -407,31 +474,94 @@ export function Composer({
         subject,
         html,
         text: htmlToText(html),
-        attachment_ids: attachments.map((a) => a.id),
+        attachment_ids: atts.map((a) => a.id),
       },
     };
   };
 
-  useEffect(() => {
-    if (undo) return;
-    const handle = window.setTimeout(async () => {
-      if (!dirtyRef.current) return; // nothing the user changed -> don't touch the draft
-      if (!to && !subject && !bodyHtml) return;
-      setStatus("saving");
+  // Keep this message on the device (offline): as a draft, or for Scheduled.
+  const saveLocal = async (state: LocalState) => {
+    localId.current ??= newLocalId();
+    const msg: LocalMessage = {
+      id: localId.current,
+      state,
+      input: payload(),
+      attachments,
+      files: localFiles,
+      serverDraftId: draftId.current,
+      updatedAt: Date.now(),
+    };
+    await putLocal(msg);
+  };
+
+  // While a copy is kept here, other tabs' hand-over to the server leaves it be.
+  const [heldId, setHeldId] = useState(localId.current);
+  useEffect(() => (heldId ? holdOpen(heldId) : undefined), [heldId]);
+
+  // Save to the server; a copy kept on this device goes there first (its files
+  // uploaded), then is dropped. Returns the attachments now on the server.
+  const saveToServer = async (): Promise<AttachmentOut[]> => {
+    let atts = attachments;
+    if (localFiles.length) {
+      const uploaded = await uploadFiles(localFiles);
+      await deleteFiles(localFiles.map((f) => f.id));
+      atts = [...attachments, ...uploaded];
+      setAttachments(atts);
+      setLocalFiles([]);
+    }
+    if (draftId.current) await api.updateDraft(draftId.current, payload(atts));
+    else draftId.current = (await api.createDraft(payload(atts))).id;
+    if (localId.current) {
+      await deleteLocal(localId.current);
+      localId.current = null;
+      setHeldId(null);
+    }
+    localState.current = "draft"; // on the server now: a draft until Send
+    return atts;
+  };
+
+  const autosave = async () => {
+    setStatus("saving");
+    try {
+      if (isOffline()) throw new ApiError(0, "offline", "offline");
+      await saveToServer();
+      setStatus("saved");
+    } catch (e) {
+      if (!isOfflineError(e)) {
+        setStatus("error");
+        return;
+      }
       try {
-        if (draftId.current) {
-          await api.updateDraft(draftId.current, payload());
-        } else {
-          draftId.current = (await api.createDraft(payload())).id;
-        }
-        setStatus("saved");
+        await saveLocal(localState.current);
+        setHeldId(localId.current);
+        setStatus("savedLocal");
       } catch {
         setStatus("error");
       }
+    }
+  };
+
+  useEffect(() => {
+    if (undo) return;
+    const handle = window.setTimeout(() => {
+      if (!dirtyRef.current) return; // nothing the user changed -> don't touch the draft
+      if (!to && !subject && !bodyHtml) return;
+      void autosave();
     }, 2000);
     return () => window.clearTimeout(handle);
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [accountId, to, cc, bcc, subject, bodyHtml, attachments]);
+  }, [accountId, to, cc, bcc, subject, bodyHtml, attachments, localFiles]);
+
+  // Back online with a draft kept here: hand it to the server now. (A
+  // scheduled one is sent by the scheduled sender once this window closes.)
+  useEffect(() => {
+    if (!offline && localId.current && !undo && localState.current === "draft") void autosave();
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [offline]);
+
+  // The latest way to save locally, for the unmount below (its closure is old).
+  const saveLocalRef = useRef(saveLocal);
+  saveLocalRef.current = saveLocal;
 
   useEffect(
     () => () => {
@@ -439,25 +569,57 @@ export function Composer({
       // On close, mirror the draft to the IMAP Drafts folder so it can be
       // continued on any mail client — but only if the user actually edited it
       // (skip if it was sent, discarded, or merely opened to view).
-      if (draftId.current && !sentRef.current && dirtyRef.current) {
+      if (localId.current && localState.current === "scheduled" && !sentRef.current && !discardedRef.current) {
+        // A scheduled message looked at (or edited offline) and closed: still
+        // scheduled — save any change, then let the sender have it.
+        const save = dirtyRef.current ? saveLocalRef.current("scheduled") : Promise.resolve();
+        void save.finally(() => window.dispatchEvent(new Event("webmail:send-scheduled")));
+        return;
+      }
+      if (sentRef.current || discardedRef.current || !dirtyRef.current) return;
+      if (isOffline()) {
+        // Closed offline: keep it here as a draft (the server gets it later).
+        void saveLocalRef.current("draft").catch(() => {});
+        return;
+      }
+      if (draftId.current && !localId.current) {
         void api.publishDraft(draftId.current).catch(() => {});
       }
     },
     [],
   );
 
+  // Offline (or the connection dropped while sending): into Scheduled, to go
+  // out on its own once the server is reachable again.
+  const schedule = async () => {
+    try {
+      await saveLocal("scheduled");
+      sentRef.current = true;
+      showOfflineNotice("scheduled", 5000);
+      onClose();
+    } catch {
+      sentRef.current = false;
+      setStatus("error");
+    }
+  };
+
   const send = async () => {
     setStatus("sending");
     sentRef.current = true; // don't also mirror to Drafts on close
+    if (isOffline()) {
+      await schedule();
+      return;
+    }
     try {
-      if (!draftId.current) draftId.current = (await api.createDraft(payload())).id;
-      else await api.updateDraft(draftId.current, payload());
-      const res = await api.send(draftId.current);
-      // Drive the countdown + auto-close off the server's undo deadline.
-      const until = new Date(res.undo_until).getTime();
+      await saveToServer();
+      const sentDraft = draftId.current!;
+      const res = await api.send(sentDraft);
+      // Drive the countdown + auto-close off the server's undo window, as a
+      // duration: this computer's clock may be seconds off the server's.
+      const until = Date.now() + res.undo_seconds * 1000;
       // With a toast to carry the undo offer, the window closes right away.
       if (hasUndoHost()) {
-        offerUndo({ outboxId: res.outbox_id, draftId: draftId.current, until });
+        offerUndo({ outboxId: res.outbox_id, draftId: sentDraft, until });
         onClose();
         return;
       }
@@ -466,6 +628,10 @@ export function Composer({
       setUndoLeft(Math.ceil(remaining / 1000));
       undoTimer.current = window.setTimeout(onClose, remaining);
     } catch (e) {
+      if (isOfflineError(e)) {
+        await schedule();
+        return;
+      }
       sentRef.current = false;
       setStatus("error");
       if (!(e instanceof ApiError)) throw e;
@@ -486,7 +652,14 @@ export function Composer({
   };
 
   const discard = async () => {
-    if (draftId.current) {
+    discardedRef.current = true;
+    if (localId.current) {
+      await deleteLocal(localId.current).catch(() => {});
+      localId.current = null;
+    } else if (localFiles.length) {
+      await deleteFiles(localFiles.map((f) => f.id)).catch(() => {});
+    }
+    if (draftId.current && !isOffline()) {
       try {
         await api.deleteDraft(draftId.current);
       } catch {
@@ -500,7 +673,7 @@ export function Composer({
   // X button: if there's a draft worth keeping, ask before closing; otherwise
   // (nothing typed, no draft) just close.
   const requestClose = () => {
-    if (!dirtyRef.current && !draftId.current) {
+    if (!dirtyRef.current && !draftId.current && !localId.current) {
       onClose();
       return;
     }
@@ -513,10 +686,7 @@ export function Composer({
   const saveDraftAndClose = async () => {
     setShowClosePrompt(false);
     try {
-      if (dirtyRef.current) {
-        if (draftId.current) await api.updateDraft(draftId.current, payload());
-        else draftId.current = (await api.createDraft(payload())).id;
-      }
+      if (dirtyRef.current) await autosave();
     } catch {
       /* the close-time IMAP mirror is best-effort too */
     }
@@ -639,7 +809,7 @@ export function Composer({
             </svg>
             {/* Phone width: the icon alone. */}
             <span className="max-md:hidden">
-              {status === "sending" ? t("compose.sending") : t("compose.send")}
+              {status === "sending" ? t("compose.sending") : offline ? t("compose.sendLater") : t("compose.send")}
             </span>
           </button>
           <HeaderButton onClick={() => fileInputRef.current?.click()} title={t("compose.attach")}>
@@ -758,6 +928,7 @@ export function Composer({
         <div className="ml-auto flex items-center gap-1 text-xs text-app-faint">
           {!minimized && status === "saving" && <span className="mr-1">{t("compose.savingDraft")}</span>}
           {!minimized && status === "saved" && <span className="mr-1">{t("compose.draftSaved")}</span>}
+          {!minimized && status === "savedLocal" && <span className="mr-1">{t("compose.savedOnDevice")}</span>}
           {!minimized && status === "error" && (
             <span className="mr-1 text-red-500">{t("compose.sendFailed")}</span>
           )}
@@ -793,7 +964,7 @@ export function Composer({
           {!fullWindow && (
             // No second browser window to pop out into on a phone.
             <div className="contents max-md:hidden">
-            <HeaderButton onClick={popOut} title={t("compose.popOut")}>
+            <HeaderButton onClick={popOut} title={t("compose.popOut")} className="wm-online-only">
               <svg width="15" height="15" viewBox="0 0 16 16" fill="none" stroke="currentColor" strokeWidth="1.4" strokeLinecap="round" strokeLinejoin="round">
                 <path d="M6 3H3v10h10v-3M9 3h4v4M13 3L7 9" />
               </svg>
@@ -898,7 +1069,7 @@ export function Composer({
           }}
         />
 
-        {(attachments.length > 0 || attachError) && (
+        {(attachments.length > 0 || localFiles.length > 0 || attachError) && (
           <div className="flex flex-wrap items-center gap-2 border-b border-app-border px-3 py-2">
             {attachments.map((att) => (
               <span
@@ -920,6 +1091,27 @@ export function Composer({
                 </button>
               </span>
             ))}
+            {localFiles.map((f) => (
+              <span
+                key={f.id}
+                title={t("compose.attachOnDevice")}
+                className="flex items-center gap-1.5 rounded border border-dashed border-app-border bg-app-hover px-2 py-1 text-xs text-app-fg"
+              >
+                <svg width="13" height="13" viewBox="0 0 16 16" fill="none" stroke="currentColor" strokeWidth="1.4" strokeLinecap="round" strokeLinejoin="round">
+                  <path d="M12.5 6.5l-5.2 5.2a2.5 2.5 0 0 1-3.5-3.5l5.4-5.4a1.6 1.6 0 0 1 2.3 2.3l-5.3 5.3a0.8 0.8 0 0 1-1.1-1.1l4.9-4.9" />
+                </svg>
+                <span className="max-w-[12rem] truncate">{f.name}</span>
+                <span className="text-app-faint">{formatBytes(f.size)}</span>
+                <button
+                  type="button"
+                  onClick={() => removeLocalFile(f.id)}
+                  className="text-app-faint hover:text-app-fg"
+                  aria-label={`remove ${f.name}`}
+                >
+                  ✕
+                </button>
+              </span>
+            ))}
             {attachError && <span className="text-xs text-red-500">{attachError}</span>}
           </div>
         )}

frontend/src/components/compose/RecipientChips.tsx

@@ -2,6 +2,7 @@ import { useEffect, useRef, useState } from "react";
 
 import { useT } from "../../i18n";
 import { api } from "../../lib/api";
+import { isOffline } from "../../lib/offline";
 import type { RecipientSuggestion } from "../../lib/types";
 
 function splitList(value: string): string[] {
@@ -76,7 +77,8 @@ export function RecipientChips({
   const removeAt = (i: number) => onChange(chips.filter((_, idx) => idx !== i).join(", "));
 
   useEffect(() => {
-    if (draft.trim().length < 2) {
+    // Suggestions come from the server: none offline (and no doomed request).
+    if (draft.trim().length < 2 || isOffline()) {
       setSuggestions([]);
       return;
     }

frontend/src/components/list/DraftsList.tsx

@@ -1,5 +1,6 @@
 import { useT } from "../../i18n";
 import { formatClock, getDateLocale } from "../../lib/timeFormat";
+import type { LocalMessage } from "../../lib/scheduled";
 import type { DraftOut, RemoteDraftOut } from "../../lib/types";
 
 function timeLabel(iso: string): string {
@@ -15,6 +16,7 @@ function DraftRow({
   preview,
   time,
   badge,
+  badgeTone,
   selected,
   onClick,
 }: {
@@ -23,9 +25,16 @@ function DraftRow({
   preview: string;
   time: string;
   badge?: string;
+  badgeTone?: "muted" | "accent" | "error";
   selected: boolean;
   onClick: () => void;
 }) {
+  const tone =
+    badgeTone === "accent"
+      ? "bg-app-accent/15 text-app-accent"
+      : badgeTone === "error"
+        ? "bg-red-500/15 text-red-500"
+        : "bg-app-hover text-app-muted";
   return (
     <button
       onClick={onClick}
@@ -36,7 +45,7 @@ function DraftRow({
       <div className="flex items-center gap-2">
         <span className="flex-1 truncate text-sm text-app-fg">{recipients}</span>
         {badge && (
-          <span className="shrink-0 rounded bg-app-hover px-1.5 text-[12px] text-app-muted">
+          <span className={`shrink-0 rounded px-1.5 text-[12px] ${tone}`}>
             {badge}
           </span>
         )}
@@ -53,20 +62,28 @@ function DraftRow({
 export function DraftsList({
   drafts,
   remoteDrafts,
+  deviceDrafts = [],
+  note,
   selectedId,
   onOpen,
   onOpenRemote,
+  onOpenDevice,
 }: {
   drafts: DraftOut[];
   remoteDrafts: RemoteDraftOut[];
+  /** Drafts written offline, kept on this device until the server has them. */
+  deviceDrafts?: LocalMessage[];
+  /** A line above the list (offline: only this device's drafts are here). */
+  note?: string;
   /** Id of the draft currently loaded in the reading pane. */
   selectedId?: string;
   onOpen: (draft: DraftOut) => void;
   onOpenRemote: (draft: RemoteDraftOut) => void;
+  onOpenDevice?: (msg: LocalMessage) => void;
 }) {
   const t = useT();
-  if (drafts.length === 0 && remoteDrafts.length === 0) {
-    return <div className="p-6 text-sm text-app-faint">{t("compose.noDrafts")}</div>;
+  if (drafts.length === 0 && remoteDrafts.length === 0 && deviceDrafts.length === 0) {
+    return <div className="p-6 text-sm text-app-faint">{note ?? t("compose.noDrafts")}</div>;
   }
 
   // Merge local + remote drafts into one list sorted by date (newest first).
@@ -80,8 +97,20 @@ export function DraftsList({
     selected: boolean;
     onClick: () => void;
   };
+  // A device draft continuing a server draft stands in for it.
+  const onDevice = new Set(deviceDrafts.map((m) => m.serverDraftId).filter(Boolean));
   const rows: Row[] = [
-    ...drafts.map((d) => ({
+    ...deviceDrafts.map((m) => ({
+      key: `d-${m.id}`,
+      date: new Date(m.updatedAt).toISOString(),
+      recipients: m.input.payload.to.join(", ") || t("compose.noRecipient"),
+      subject: m.input.payload.subject || t("compose.noSubject"),
+      preview: m.input.payload.text.trim(),
+      badge: t("compose.onDevice"),
+      selected: m.id === selectedId,
+      onClick: () => onOpenDevice?.(m),
+    })),
+    ...drafts.filter((d) => !onDevice.has(d.id)).map((d) => ({
       key: `l-${d.id}`,
       date: d.updated_at,
       recipients: d.payload.to.join(", ") || t("compose.noRecipient"),
@@ -106,6 +135,7 @@ export function DraftsList({
 
   return (
     <div className="h-full overflow-y-auto" data-testid="drafts-list">
+      {note && <div className="border-b border-app-border px-6 py-2 text-xs text-app-faint">{note}</div>}
       {rows.map((row) => (
         <DraftRow
           key={row.key}
@@ -121,3 +151,43 @@ export function DraftsList({
     </div>
   );
 }
+
+// The Scheduled folder: messages sent while offline, waiting for the connection.
+export function ScheduledList({
+  messages,
+  selectedId,
+  onOpen,
+}: {
+  messages: LocalMessage[];
+  selectedId?: string;
+  onOpen: (msg: LocalMessage) => void;
+}) {
+  const t = useT();
+  if (messages.length === 0) {
+    return <div className="p-6 text-sm text-app-faint">{t("scheduled.empty")}</div>;
+  }
+  return (
+    <div className="h-full overflow-y-auto" data-testid="scheduled-list">
+      <div className="border-b border-app-border px-6 py-2 text-xs text-app-faint">{t("scheduled.help")}</div>
+      {messages.map((m) => (
+        <DraftRow
+          key={m.id}
+          recipients={m.input.payload.to.join(", ") || t("compose.noRecipient")}
+          subject={m.input.payload.subject || t("compose.noSubject")}
+          preview={m.state === "failed" && m.error ? m.error : m.input.payload.text.trim()}
+          time={timeLabel(new Date(m.updatedAt).toISOString())}
+          badge={
+            m.state === "failed"
+              ? t("scheduled.failed")
+              : m.state === "sending"
+                ? t("scheduled.sending")
+                : t("scheduled.waiting")
+          }
+          badgeTone={m.state === "failed" ? "error" : "accent"}
+          selected={m.id === selectedId}
+          onClick={() => onOpen(m)}
+        />
+      ))}
+    </div>
+  );
+}

frontend/src/components/thread/ThreadView.tsx

@@ -343,7 +343,7 @@ function MessageItem({
   const [showDetails, setShowDetails] = useState(false);
   const replyBtn = (kind: string, label: string, icon: string) => (
     <button
-      className="wm-online-only flex items-center gap-1.5 rounded-md border border-app-border px-3 py-1.5 text-xs text-app-fg hover:bg-app-hover"
+      className="flex items-center gap-1.5 rounded-md border border-app-border px-3 py-1.5 text-xs text-app-fg hover:bg-app-hover"
       onClick={() => onReply(kind)}
     >
       <Icon name={icon} size={14} />
@@ -442,7 +442,7 @@ function MessageItem({
                   </button>
                   {canReply && (
                     <button
-                      className="wm-online-only flex items-center gap-1 text-app-muted hover:text-app-fg"
+                      className="flex items-center gap-1 text-app-muted hover:text-app-fg"
                       onClick={() => onReply(multiRecipient ? "reply_all" : "reply")}
                     >
                       <Icon name={multiRecipient ? "reply-all" : "reply"} size={14} />

frontend/src/i18n/en.ts

@@ -556,6 +556,19 @@ export const en = {
   "offline.notAvailable": "Not available offline",
   "offline.threadNotSaved": "This conversation isn't saved on this device.",
   "offline.folderNotSaved": "This folder isn't saved on this device.",
+  "offline.noticeScheduled": "Saved to Scheduled — it will be sent when you're back online.",
+  "offline.noticeSendingScheduled": "Sending {count} scheduled messages…",
+  "offline.draftsNotSaved": "Only drafts written on this device are available offline.",
+  "compose.sendLater": "Schedule",
+  "compose.savedOnDevice": "Saved on this device",
+  "compose.attachOnDevice": "On this device — uploaded when you're back online",
+  "compose.onDevice": "On this device",
+  "nav.scheduled": "Scheduled",
+  "scheduled.help": "Sent automatically when you're back online.",
+  "scheduled.empty": "Nothing scheduled.",
+  "scheduled.waiting": "Waiting",
+  "scheduled.sending": "Sending…",
+  "scheduled.failed": "Not sent",
   "offline.searchPlaceholder": "Search (offline)",
   "offline.cantReach": "Can't reach the server.",
   "offline.settingTitle": "Offline access",

frontend/src/lib/auth.ts

@@ -2,6 +2,7 @@ import { type QueryClient, useQuery } from "@tanstack/react-query";
 
 import { api, ApiError } from "./api";
 import { clearOfflineData } from "./offline";
+import { wipeLocal } from "./scheduled";
 
 export function useMe() {
   return useQuery({
@@ -26,6 +27,7 @@ export function signedOut(queryClient: QueryClient) {
   // whole cache first would orphan them from the query they watch.
   queryClient.setQueryData(["me"], null);
   void clearOfflineData(); // mail saved for offline reading goes with the session
+  void wipeLocal(); // and so does anything written offline
   queryClient.removeQueries({ predicate: (q) => q.queryKey[0] !== "me" });
 }
 

frontend/src/lib/offlineNotice.ts

@@ -0,0 +1,54 @@
+// The short-lived offline messages (components/Offline.tsx shows them): the
+// floating notice at the bottom, and the green "Back online" in the sidebar.
+// Their own module so anything — the composer, the scheduled sender — can raise one.
+
+import { useSyncExternalStore } from "react";
+
+export type NoticeKey = "offline" | "offlineNotSaved" | "notAvailable" | "scheduled" | "sendingScheduled";
+
+export interface Notice {
+  key: NoticeKey;
+  vars?: Record<string, string | number>;
+  seq: number;
+}
+
+let notice: Notice | null = null;
+let backOnline = false;
+const listeners = new Set<() => void>();
+const emit = () => listeners.forEach((l) => l());
+const subscribe = (l: () => void) => {
+  listeners.add(l);
+  return () => {
+    listeners.delete(l);
+  };
+};
+let noticeTimer: number | undefined;
+let noticeSeq = 0;
+
+export function showOfflineNotice(key: NoticeKey, ms: number, vars?: Notice["vars"]): void {
+  notice = { key, vars, seq: ++noticeSeq };
+  emit();
+  window.clearTimeout(noticeTimer);
+  noticeTimer = window.setTimeout(() => {
+    notice = null;
+    emit();
+  }, ms);
+}
+
+export function clearOfflineNotice(): void {
+  notice = null;
+  emit();
+}
+
+export function useOfflineNotice(): Notice | null {
+  return useSyncExternalStore(subscribe, () => notice);
+}
+
+export function setBackOnline(value: boolean): void {
+  backOnline = value;
+  emit();
+}
+
+export function useBackOnline(): boolean {
+  return useSyncExternalStore(subscribe, () => backOnline);
+}

frontend/src/lib/scheduled.ts

@@ -0,0 +1,274 @@
+// Messages written while offline, kept on this device (IndexedDB) until the
+// server can take them:
+//  - "draft": written offline and not sent — becomes a normal server draft
+//    once the connection is back;
+//  - "scheduled": Send was pressed offline — sent as soon as the connection is
+//    back (the "Scheduled" folder);
+//  - "sending": being handed to the server right now;
+//  - "failed": the server refused it (shown in Scheduled with the reason).
+//
+// Files attached offline are kept here too, and uploaded when the message goes
+// to the server. Nothing here leaves this device until then.
+
+import { useEffect, useSyncExternalStore } from "react";
+
+import { api, ApiError, isOfflineError } from "./api";
+import type { AttachmentOut, DraftInput } from "./types";
+
+export type LocalState = "draft" | "scheduled" | "sending" | "failed";
+
+export interface LocalFile {
+  id: string;
+  name: string;
+  type: string;
+  size: number;
+}
+
+export interface LocalMessage {
+  id: string;
+  state: LocalState;
+  /** The draft as the server takes it; attachment_ids are server attachments. */
+  input: DraftInput;
+  /** Those server attachments' names and sizes, to show them offline. */
+  attachments: AttachmentOut[];
+  /** Files attached offline, uploaded when the message reaches the server. */
+  files: LocalFile[];
+  /** The server draft this continues (opened from Drafts, then went offline). */
+  serverDraftId: string | null;
+  error?: string;
+  updatedAt: number;
+}
+
+export interface ScheduledSent {
+  outboxId: string;
+  draftId: string;
+  undoSeconds: number;
+}
+
+const DB_NAME = "wm-offline";
+const MESSAGES = "messages";
+const FILES = "files";
+
+// ---- IndexedDB, promised ---------------------------------------------------------
+
+let dbPromise: Promise<IDBDatabase> | null = null;
+
+function db(): Promise<IDBDatabase> {
+  dbPromise ??= new Promise((resolve, reject) => {
+    const req = indexedDB.open(DB_NAME, 1);
+    req.onupgradeneeded = () => {
+      req.result.createObjectStore(MESSAGES, { keyPath: "id" });
+      req.result.createObjectStore(FILES, { keyPath: "id" });
+    };
+    req.onsuccess = () => resolve(req.result);
+    req.onerror = () => {
+      dbPromise = null;
+      reject(req.error);
+    };
+  });
+  return dbPromise;
+}
+
+function done<T>(req: IDBRequest<T>): Promise<T> {
+  return new Promise((resolve, reject) => {
+    req.onsuccess = () => resolve(req.result);
+    req.onerror = () => reject(req.error);
+  });
+}
+
+async function store(name: string, mode: IDBTransactionMode): Promise<IDBObjectStore> {
+  return (await db()).transaction(name, mode).objectStore(name);
+}
+
+// ---- change notification (this tab, and the others) -------------------------------
+
+const listeners = new Set<() => void>();
+const channel = "BroadcastChannel" in window ? new BroadcastChannel("wm-local-messages") : null;
+let snapshot: LocalMessage[] = [];
+let loaded = false;
+
+async function reload(): Promise<void> {
+  try {
+    const all = (await done((await store(MESSAGES, "readonly")).getAll())) as LocalMessage[];
+    snapshot = all.sort((a, b) => b.updatedAt - a.updatedAt);
+  } catch {
+    snapshot = [];
+  }
+  loaded = true;
+  for (const l of listeners) l();
+}
+
+function changed(): void {
+  channel?.postMessage("changed");
+  void reload();
+}
+
+channel?.addEventListener("message", () => void reload());
+
+/** Everything kept on this device, newest first (live). */
+export function useLocalMessages(): LocalMessage[] {
+  useEffect(() => {
+    if (!loaded) void reload();
+  }, []);
+  return useSyncExternalStore(
+    (l) => {
+      listeners.add(l);
+      return () => {
+        listeners.delete(l);
+      };
+    },
+    () => snapshot,
+  );
+}
+
+// ---- reading and writing ---------------------------------------------------------
+
+export function newLocalId(): string {
+  return `local-${crypto.randomUUID()}`;
+}
+
+export async function listLocal(): Promise<LocalMessage[]> {
+  return (await done((await store(MESSAGES, "readonly")).getAll())) as LocalMessage[];
+}
+
+export async function putLocal(msg: LocalMessage): Promise<void> {
+  await done((await store(MESSAGES, "readwrite")).put(msg));
+  changed();
+}
+
+export async function deleteLocal(id: string): Promise<void> {
+  const msg = (await done((await store(MESSAGES, "readonly")).get(id))) as LocalMessage | undefined;
+  if (msg) await deleteFiles(msg.files.map((f) => f.id));
+  await done((await store(MESSAGES, "readwrite")).delete(id));
+  changed();
+}
+
+/** Keep a file attached offline; returns what the composer shows for it. */
+export async function putFile(file: File): Promise<LocalFile> {
+  const meta = { id: crypto.randomUUID(), name: file.name, type: file.type, size: file.size };
+  await done((await store(FILES, "readwrite")).put({ ...meta, blob: file }));
+  return meta;
+}
+
+export async function deleteFiles(ids: string[]): Promise<void> {
+  if (!ids.length) return;
+  const s = await store(FILES, "readwrite");
+  await Promise.all(ids.map((id) => done(s.delete(id))));
+}
+
+async function getFile(meta: LocalFile): Promise<File | null> {
+  const row = (await done((await store(FILES, "readonly")).get(meta.id))) as
+    | (LocalFile & { blob: Blob })
+    | undefined;
+  return row ? new File([row.blob], meta.name, { type: meta.type }) : null;
+}
+
+/** Upload files attached offline; returns the server attachments they became. */
+export async function uploadFiles(files: LocalFile[]): Promise<AttachmentOut[]> {
+  const out: AttachmentOut[] = [];
+  for (const meta of files) {
+    const file = await getFile(meta);
+    if (file) out.push(await api.uploadComposeAttachment(file));
+  }
+  return out;
+}
+
+/** Forget everything kept here (signed out: it must not outlive the session). */
+export async function wipeLocal(): Promise<void> {
+  try {
+    await done((await store(MESSAGES, "readwrite")).clear());
+    await done((await store(FILES, "readwrite")).clear());
+  } catch {
+    /* nothing kept */
+  }
+  changed();
+}
+
+// Composer windows holding a local message open: those save it themselves.
+const openHere = new Set<string>();
+
+export function holdOpen(id: string): () => void {
+  openHere.add(id);
+  return () => {
+    openHere.delete(id);
+  };
+}
+
+// ---- handing everything to the server -------------------------------------------
+
+/** Make a local message a server draft (files uploaded first); returns its id. */
+async function toServerDraft(msg: LocalMessage): Promise<string> {
+  if (msg.files.length) {
+    const uploaded = await uploadFiles(msg.files);
+    await deleteFiles(msg.files.map((f) => f.id));
+    msg.attachments = [...msg.attachments, ...uploaded];
+    msg.input = {
+      ...msg.input,
+      payload: { ...msg.input.payload, attachment_ids: msg.attachments.map((a) => a.id) },
+    };
+    msg.files = [];
+    await putLocal(msg); // never upload the same files twice
+  }
+  if (msg.serverDraftId) {
+    await api.updateDraft(msg.serverDraftId, msg.input);
+  } else {
+    msg.serverDraftId = (await api.createDraft(msg.input)).id;
+    await putLocal(msg); // and never create the draft twice
+  }
+  return msg.serverDraftId;
+}
+
+async function flushOne(msg: LocalMessage, sent: ScheduledSent[]): Promise<void> {
+  if (msg.state === "draft") {
+    const id = await toServerDraft(msg);
+    void api.publishDraft(id).catch(() => {}); // like a composer closed online
+    await deleteLocal(msg.id);
+    return;
+  }
+  msg.state = "sending";
+  await putLocal(msg);
+  try {
+    const draftId = await toServerDraft(msg);
+    const res = await api.send(draftId);
+    await deleteLocal(msg.id);
+    sent.push({ outboxId: res.outbox_id, draftId, undoSeconds: res.undo_seconds });
+  } catch (err) {
+    msg.state = isOfflineError(err) ? "scheduled" : "failed";
+    msg.error = err instanceof ApiError ? err.message : String(err);
+    await putLocal(msg);
+    throw err;
+  }
+}
+
+let flushing: Promise<ScheduledSent[]> | null = null;
+
+/**
+ * Hand everything kept here to the server: scheduled messages are sent, drafts
+ * become server drafts. Under a lock, so two open tabs never send one message
+ * twice. Stops at the first sign of being offline again.
+ */
+export function flushLocal(): Promise<ScheduledSent[]> {
+  const run = async (): Promise<ScheduledSent[]> => {
+    const sent: ScheduledSent[] = [];
+    const all = (await listLocal()).sort((a, b) => a.updatedAt - b.updatedAt);
+    for (const msg of all) {
+      if (msg.state === "failed") continue;
+      if (openHere.has(msg.id)) continue; // open in a composer here: it decides
+      try {
+        await flushOne(msg, sent);
+      } catch (err) {
+        if (isOfflineError(err)) break;
+      }
+    }
+    return sent;
+  };
+  flushing ??= (async () => {
+    try {
+      const locks = (navigator as Navigator & { locks?: LockManager }).locks;
+      return locks ? await locks.request("wm-local-flush", run) : await run();
+    } finally {
+      flushing = null;
+    }
+  })();
+  return flushing;
+}

frontend/src/lib/types.ts

@@ -308,6 +308,8 @@ export interface DraftOut {
 export interface SendResponse {
   outbox_id: string;
   undo_until: string;
+  /** Seconds left in the undo window (count down from this, not the clock). */
+  undo_seconds: number;
 }
 
 export interface RemoteDraftOut {

frontend/src/routes/MailLayout.tsx

@@ -1,11 +1,11 @@
 import { keepPreviousData, useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
-import { useCallback, useEffect, useRef, useState } from "react";
+import { Fragment, useCallback, useEffect, useRef, useState } from "react";
 import { Link, useMatch, useNavigate, useSearchParams } from "react-router-dom";
 
 import signetLogo from "../../icons/ultimo-logo-signet.svg";
 import { AppSwitcher } from "../components/AppSwitcher";
 import { ComposeDock } from "../components/compose/ComposeDock";
-import { Composer, type ComposerInit, draftToInit } from "../components/compose/Composer";
+import { Composer, type ComposerInit, draftToInit, localToInit } from "../components/compose/Composer";
 import { UndoSendToast } from "../components/compose/UndoSendToast";
 import { usePendingSend } from "../components/compose/undoSend";
 import {
@@ -17,14 +17,14 @@ import {
   restoreWindow,
   toggleExpand,
 } from "../components/compose/windows";
-import { DraftsList } from "../components/list/DraftsList";
+import { DraftsList, ScheduledList } from "../components/list/DraftsList";
 import { Icon } from "../components/Icon";
 import { MessageList } from "../components/list/MessageList";
 import { Resizer } from "../components/Resizer";
 import { ThemeToggle } from "../components/ThemeToggle";
 import { EmptyIllustration } from "../components/EmptyIllustration";
 import { BackfillBanner } from "../components/BackfillBanner";
-import { NotSavedOffline, OfflineIndicator } from "../components/Offline";
+import { Clock, NotSavedOffline, OfflineIndicator } from "../components/Offline";
 import { ThreadView } from "../components/thread/ThreadView";
 import { MailboxDisplay } from "../components/mail/MailboxDisplay";
 import { RightPanel, type PanelTab } from "../components/mail/RightPanel";
@@ -32,6 +32,7 @@ import { useT } from "../i18n";
 import type { MessageKey } from "../i18n/en";
 import { api, isOfflineError } from "../lib/api";
 import { clearOfflineData, useOffline } from "../lib/offline";
+import { flushLocal, useLocalMessages, wipeLocal } from "../lib/scheduled";
 import { setTimeFormat } from "../lib/timeFormat";
 import type { QuotaOut, SavedSearch, ThreadSummary } from "../lib/types";
 import { useReadingPane } from "../lib/readingPane";
@@ -217,6 +218,12 @@ export function MailLayout() {
   useEffect(() => localStorage.setItem("mail.listOrder", listOrder), [listOrder]);
 
   const isDrafts = view === "folder:drafts";
+  // Messages written offline: drafts kept on this device, and the Scheduled
+  // folder of ones sent offline (lib/scheduled.ts).
+  const isScheduled = view === "local:scheduled";
+  const localMessages = useLocalMessages();
+  const deviceDrafts = localMessages.filter((m) => m.state === "draft");
+  const scheduled = localMessages.filter((m) => m.state !== "draft");
   // Which special-use folder the reading pane is showing (drives the toolbar).
   const currentFolder = view.startsWith("folder:") ? view.slice("folder:".length) : "inbox";
   const accountsQuery = useQuery({ queryKey: ["accounts"], queryFn: api.accounts });
@@ -233,7 +240,7 @@ export function MailLayout() {
       }
       return api.threads(view, { offset: page * PAGE_SIZE, limit: PAGE_SIZE, filter, order: orderParam });
     },
-    enabled: !isDrafts && !searching,
+    enabled: !isDrafts && !isScheduled && !searching,
     placeholderData: keepPreviousData, // keep the current page visible while the next loads
   });
   const draftsQuery = useQuery({
@@ -798,7 +805,7 @@ export function MailLayout() {
         </div>
         <div className={`pb-2 pt-2.5 ${collapsed ? "px-2" : "px-3"} ${mobile ? "hidden" : ""}`}>
           <button
-            className="wm-online-only flex w-full items-center justify-center gap-2 rounded-lg bg-app-accent py-2 text-[15px] font-medium text-app-accent-fg shadow-sm hover:opacity-90"
+            className="flex w-full items-center justify-center gap-2 rounded-lg bg-app-accent py-2 text-[15px] font-medium text-app-accent-fg shadow-sm hover:opacity-90"
             title={collapsed ? t("nav.compose") : undefined}
             onClick={() => accounts[0] && openComposer({ accountId: accounts[0].id, kind: "new" })}
           >
@@ -812,11 +819,11 @@ export function MailLayout() {
               f.view === "folder:inbox"
                 ? countsQuery.data?.inbox_unread
                 : f.view === "folder:drafts"
-                  ? countsQuery.data?.drafts
+                  ? (countsQuery.data?.drafts ?? 0) + deviceDrafts.length || undefined
                   : undefined;
             return (
+            <Fragment key={f.view}>
             <SidebarItem
-              key={f.view}
               active={view === f.view}
               collapsed={collapsed}
               title={collapsed ? t(f.label) : undefined}
@@ -828,6 +835,24 @@ export function MailLayout() {
                 <span className="ml-auto shrink-0 tabular-nums text-[13px] text-app-muted">{badge}</span>
               ) : null}
             </SidebarItem>
+            {/* Scheduled: shown while something waits to be sent (or is open). */}
+            {f.view === "folder:drafts" && (scheduled.length > 0 || isScheduled) && (
+              <SidebarItem
+                active={isScheduled}
+                collapsed={collapsed}
+                title={collapsed ? t("nav.scheduled") : undefined}
+                onClick={() => selectView("local:scheduled")}
+              >
+                <span className="flex w-[18px] justify-center">
+                  <Clock size={18} />
+                </span>
+                {!collapsed && <span className="flex-1 truncate">{t("nav.scheduled")}</span>}
+                {!collapsed && scheduled.length > 0 && (
+                  <span className="ml-auto shrink-0 tabular-nums text-[13px] text-app-muted">{scheduled.length}</span>
+                )}
+              </SidebarItem>
+            )}
+            </Fragment>
             );
           })}
           {/* Per-account views are hidden entirely when collapsed. */}
@@ -912,8 +937,12 @@ export function MailLayout() {
             }`}
             title={collapsed ? t("common.signOut") : undefined}
             onClick={async () => {
+              // Anything still waiting in Scheduled goes out first: what is
+              // kept on this device is wiped with the session.
+              await flushLocal().catch(() => []);
               await api.logout();
               await clearOfflineData();
+              await wipeLocal();
               queryClient.clear();
               navigate("/login");
             }}
@@ -1036,7 +1065,7 @@ export function MailLayout() {
             </button>
           )}
         </div>
-        {!isDrafts && (
+        {!isDrafts && !isScheduled && (
           <div
             className={`flex h-[52px] shrink-0 items-center gap-5 border-b border-app-border bg-app-bg text-[15px] ${
               mobile ? "px-3" : "px-6"
@@ -1156,14 +1185,23 @@ export function MailLayout() {
           </div>
         )}
         <div className="min-h-0 flex-1">
-          {isDrafts && !term.trim() && !draftsQuery.data && isOfflineError(draftsQuery.error) ? (
-            <div className="p-6 text-[15px] text-app-faint">{t("offline.folderNotSaved")}</div>
+          {isScheduled ? (
+            <ScheduledList
+              messages={scheduled}
+              selectedId={paneDraft?.localId}
+              onOpen={(msg) => openDraftInPane(localToInit(msg))}
+            />
           ) : isDrafts && !term.trim() ? (
             <DraftsList
               drafts={draftsQuery.data ?? []}
               remoteDrafts={remoteDraftsQuery.data ?? []}
-              selectedId={paneDraft?.draftId}
+              deviceDrafts={deviceDrafts}
+              note={
+                !draftsQuery.data && isOfflineError(draftsQuery.error) ? t("offline.draftsNotSaved") : undefined
+              }
+              selectedId={paneDraft?.localId ?? paneDraft?.draftId}
               onOpen={(draft) => openDraftInPane(draftToInit(draft))}
+              onOpenDevice={(msg) => openDraftInPane(localToInit(msg))}
               onOpenRemote={async (remote) => {
                 // Adopt the server draft into an editable local draft, then open it.
                 const draft = await api.adoptDraft(remote.message_id);
@@ -1210,7 +1248,7 @@ export function MailLayout() {
           >
             <RefreshIcon spinning={refreshing} size={mobile ? 22.5 : 15} />
           </button>
-          {!isDrafts && total > 0 ? (
+          {!isDrafts && !isScheduled && total > 0 ? (
             <div className="flex items-center gap-3">
               <span>
                 {pageStart + 1}–{pageEnd} of {total}
@@ -1242,7 +1280,7 @@ export function MailLayout() {
             title={t("nav.compose")}
             aria-label={t("nav.compose")}
             onClick={() => accounts[0] && openComposer({ accountId: accounts[0].id, kind: "new" })}
-            className="wm-online-only absolute bottom-[calc(4rem+env(safe-area-inset-bottom))] right-4 z-30 flex h-14 w-14 items-center justify-center rounded-2xl bg-app-accent text-app-accent-fg shadow-lg active:opacity-90"
+            className="absolute bottom-[calc(4rem+env(safe-area-inset-bottom))] right-4 z-30 flex h-14 w-14 items-center justify-center rounded-2xl bg-app-accent text-app-accent-fg shadow-lg active:opacity-90"
           >
             <Icon name="compose" size={22} />
           </button>
@@ -1265,7 +1303,7 @@ export function MailLayout() {
           // Keyed by draft: picking a different one must build a fresh editor,
           // because RichTextEditor seeds its body exactly once.
           <Composer
-            key={paneDraft.draftId}
+            key={paneDraft.localId ?? paneDraft.draftId}
             init={paneDraft}
             onClose={closePaneDraft}
             fullWindow