diff --git a/web/src/views/mail/ThreadView.tsx b/web/src/views/mail/ThreadView.tsx
index a9dfc65..44783a8 100644
--- a/web/src/views/mail/ThreadView.tsx
+++ b/web/src/views/mail/ThreadView.tsx
@@ -224,7 +224,23 @@ export function ThreadView({ threadId, mailboxId, onBack, actions, onNavigate, h
   }, [messages, reply]);
 
   const subject = messages[0]?.subject || emails[thread?.emailIds[0] ?? ""]?.subject || "(no subject)";
-  const rowIds = thread ? thread.emailIds.filter((id) => emails[id]) : [];
+  /*
+   * What the toolbar acts on: the messages the pane is showing, not the thread
+   * they belong to.
+   *
+   * With conversation view off, opening a message opens that message -- the
+   * list shows it alone, the pane renders it alone, and the buttons above it
+   * said so, because `anyUnread` and the rest already read `messages`. Only the
+   * ids handed to the action still named the whole thread, so Mark as unread,
+   * Move to, Report spam and Delete quietly took every message in it (#414).
+   *
+   * Same fallback as the pane's: an id naming nothing in this thread means the
+   * whole conversation, so the buttons keep matching what is on screen.
+   */
+  const rowIds = useMemo(() => {
+    const loaded = thread ? thread.emailIds.filter((id) => emails[id]).map((id) => ({ id })) : [];
+    return visibleMessages(loaded, messageId).map((m) => m.id);
+  }, [thread, emails, messageId]);
   const anyUnread = messages.some((e) => !e.keywords.$seen);
   const anyStarred = messages.some((e) => e.keywords.$flagged);
   const inJunk = Boolean(mailboxId && mailboxes[mailboxId]?.role === "junk");
diff --git a/web/src/views/mail/__tests__/thread-toolbar-scope.test.tsx b/web/src/views/mail/__tests__/thread-toolbar-scope.test.tsx
new file mode 100644
index 0000000..24cf3c0
--- /dev/null
+++ b/web/src/views/mail/__tests__/thread-toolbar-scope.test.tsx
@@ -0,0 +1,128 @@
+import { act } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { ThreadView } from "../ThreadView";
+import { useMail } from "@/store/mail";
+import type { ListActions } from "../MessageList";
+import type { Email, Id } from "@/jmap/types";
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+/* jsdom has neither of these, and the opening scroll uses both. */
+Element.prototype.scrollIntoView = () => {};
+globalThis.ResizeObserver ??= class { observe() {} unobserve() {} disconnect() {} } as unknown as typeof ResizeObserver;
+
+/* jsdom has no matchMedia, and the toolbar asks whether this is a phone. */
+window.matchMedia = ((q: string) => ({ matches: false, media: q, addEventListener() {}, removeEventListener() {} })) as unknown as typeof window.matchMedia;
+
+/*
+ * Reported from the inbox with conversation view off: marking a message unread
+ * from the list -- hover button, right-click menu -- touched that message, but
+ * the same action from the toolbar above the *opened* message marked every
+ * message in its thread. Move to, Report spam and Delete did it too (#414).
+ *
+ * The toolbar's labels were already right: "Mark as unread" read the messages
+ * on screen. Only the ids it handed the action named the whole thread.
+ */
+
+const msg = (id: Id, subject: string): Email =>
+  ({
+    id, threadId: "t1", subject, mailboxIds: { inbox: true }, keywords: { $seen: true },
+    from: [{ name: "Ann", email: "ann@example.com" }], to: [{ name: "Me", email: "me@example.org" }],
+    receivedAt: "2026-09-20T10:00:00Z", size: 10, blobId: "b1", preview: "hi",
+    htmlBody: [], textBody: [{ partId: "1", type: "text/plain" }],
+    bodyValues: { "1": { value: "hi", isEncodingProblem: false, isTruncated: false } },
+    attachments: [],
+  }) as unknown as Email;
+
+const FIRST = msg("m1", "The question");
+const SECOND = msg("m2", "Re: The question");
+
+function stubStore() {
+  useMail.setState({
+    accountId: "a1",
+    threads: { t1: { id: "t1", emailIds: ["m1", "m2"] } } as never,
+    emails: { m1: FIRST, m2: SECOND } as never,
+    fullIds: { m1: true, m2: true } as never,
+    loadingThreads: {} as never,
+    mailboxes: { inbox: { id: "inbox", name: "Inbox", role: "inbox" } } as never,
+    loadThread: (async () => undefined) as never,
+    setOpenThread: (() => undefined) as never,
+    markRead: (async () => undefined) as never,
+    roleId: (() => null) as never,
+  });
+}
+
+describe("what the toolbar above an opened message acts on", () => {
+  let host: HTMLDivElement;
+  let root: Root;
+  let actions: ListActions;
+
+  const show = async (messageId: Id | null) => {
+    await act(async () => {
+      root.render(
+        <ThreadView
+          threadId="t1" mailboxId="inbox" messageId={messageId} actions={actions}
+          onBack={() => undefined} onNavigate={() => undefined} hasPrev={false} hasNext={false}
+        />,
+      );
+    });
+  };
+
+  /** The toolbar buttons carry their shortcut in the title, as the tooltips show. */
+  const press = async (title: string) => {
+    const btn = [...host.querySelectorAll("button")].find((b) => b.title === title);
+    expect(btn, `no toolbar button titled ${title}`).toBeTruthy();
+    await act(async () => btn!.click());
+  };
+
+  beforeEach(() => {
+    stubStore();
+    actions = {
+      archive: vi.fn(async () => undefined), trash: vi.fn(async () => undefined),
+      spam: vi.fn(async () => undefined), read: vi.fn(async () => undefined),
+      star: vi.fn(async () => undefined), move: vi.fn(async () => undefined),
+      label: vi.fn(async () => undefined),
+    } as unknown as ListActions;
+    host = document.createElement("div");
+    document.body.appendChild(host);
+    root = createRoot(host);
+  });
+
+  afterEach(async () => {
+    await act(async () => root.unmount());
+    host.remove();
+  });
+
+  it("marks only the message that is open, not its thread", async () => {
+    await show("m1");
+    await press("Mark as unread");
+    expect(actions.read).toHaveBeenCalledWith(false, ["m1"]);
+  });
+
+  it("moves, reports and deletes only that message too", async () => {
+    await show("m1");
+    await press("Move to (v)");
+    await press("Report spam (!)");
+    await press("Delete (#)");
+    expect(actions.move).toHaveBeenCalledWith(["m1"]);
+    expect(actions.spam).toHaveBeenCalledWith(["m1"]);
+    expect(actions.trash).toHaveBeenCalledWith(["m1"]);
+  });
+
+  it("takes the whole thread when the pane is showing the whole thread", async () => {
+    // Conversation view on: no message singled out, and the toolbar is the
+    // conversation's toolbar. That is the behaviour this must not disturb.
+    await show(null);
+    await press("Mark as unread");
+    expect(actions.read).toHaveBeenCalledWith(false, ["m1", "m2"]);
+  });
+
+  it("falls back to the thread when the open id names nothing in it", async () => {
+    // A link from somebody with conversation view on, or a stale `m` in the
+    // URL. The pane shows the conversation, so the toolbar acts on it.
+    await show("gone");
+    await press("Mark as unread");
+    expect(actions.read).toHaveBeenCalledWith(false, ["m1", "m2"]);
+  });
+});