diff --git a/src/lib/accountSettings.ts b/src/lib/accountSettings.ts
new file mode 100644
index 0000000..913067b
--- /dev/null
+++ b/src/lib/accountSettings.ts
@@ -0,0 +1,217 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+/**
+ * The theme follows the account, the same way INBUXA webmail's does: from
+ * `settings.json` in the account's own JMAP Files, inside the `ihasmail`
+ * folder. The two apps read and write the same keys, so a palette picked in
+ * either is the one both open with, on any device.
+ *
+ * The admin touches only the theme's keys: `palette`, `mode`, and the derived
+ * `theme` that older webmail builds read. Everything else in the file is the
+ * webmail's and is written back exactly as it was read, from a fresh read
+ * made just before each write. localStorage stays as the cache that paints
+ * the first frame, as in the webmail.
+ */
+import { apiFetch } from '@/services/api';
+import { jmapRequest } from '@/services/jmap/client';
+import { isPaletteId, type PaletteId } from '@/lib/palettes';
+
+const FILENODE = 'urn:ietf:params:jmap:filenode';
+const APP_FOLDER = 'ihasmail';
+const FILE = 'settings.json';
+const TYPE = 'application/json';
+const DEBOUNCE_MS = 1500;
+
+type Mode = 'system' | 'light' | 'dark';
+
+interface Target {
+  accountId: string;
+  uploadUrl: string;
+  downloadUrl: string;
+}
+
+let target: Target | null = null;
+let timer: ReturnType<typeof setTimeout> | null = null;
+/** `mode` is set only when the user picked light or dark; a palette change keeps the stored mode. */
+interface Choice {
+  palette: PaletteId;
+  mode: Mode | null;
+  fallbackMode: Mode;
+}
+let pending: Choice | null = null;
+let chain: Promise<void> = Promise.resolve();
+
+/** A server URL, as a path for apiFetch (which adds the API base). */
+function pathOf(url: string): string {
+  try {
+    const u = new URL(url, 'http://placeholder');
+    return u.pathname + u.search;
+  } catch {
+    return url;
+  }
+}
+
+/** Remember where the account's Files are, from the JMAP session. Null turns syncing off. */
+export function setAccountSettingsTarget(session: Record<string, unknown> | null): void {
+  const primary = (session?.primaryAccounts ?? {}) as Record<string, string>;
+  const accountId = primary[FILENODE];
+  const uploadUrl = session?.uploadUrl;
+  const downloadUrl = session?.downloadUrl;
+  target =
+    accountId && typeof uploadUrl === 'string' && typeof downloadUrl === 'string'
+      ? { accountId, uploadUrl, downloadUrl }
+      : null;
+  if (!target) {
+    pending = null;
+    if (timer) clearTimeout(timer);
+    timer = null;
+  }
+}
+
+async function call<T>(method: string, args: Record<string, unknown>): Promise<T> {
+  const [res] = await jmapRequest([[method, args, '0']], undefined, [FILENODE]);
+  if (!res || res[0] === 'error') throw new Error(`${method} failed`);
+  return res[1] as T;
+}
+
+interface Node {
+  id: string;
+  name: string;
+  parentId?: string | null;
+  nodeType?: string;
+  blobId?: string | null;
+}
+
+async function children(t: Target, parentId: string | null): Promise<Node[]> {
+  const filter = parentId ? { parentId } : { isTopLevel: true };
+  const responses = await jmapRequest(
+    [
+      ['FileNode/query', { accountId: t.accountId, filter, limit: 1000 }, 'q'],
+      [
+        'FileNode/get',
+        {
+          accountId: t.accountId,
+          '#ids': { resultOf: 'q', name: 'FileNode/query', path: '/ids' },
+          properties: ['id', 'name', 'parentId', 'nodeType', 'blobId'],
+        },
+        'g',
+      ],
+    ],
+    undefined,
+    [FILENODE],
+  );
+  const get = responses.find((r) => r[2] === 'g');
+  if (!get || get[0] === 'error') throw new Error('FileNode/get failed');
+  return ((get[1] as { list?: Node[] }).list ?? []) as Node[];
+}
+
+async function findFolder(t: Target): Promise<string | null> {
+  const top = await children(t, null);
+  return top.find((n) => n.name === APP_FOLDER && !n.parentId && n.nodeType === 'directory')?.id ?? null;
+}
+
+async function readFile(
+  t: Target,
+  folderId: string | null,
+): Promise<{ node: Node | null; body: Record<string, unknown> }> {
+  if (!folderId) return { node: null, body: {} };
+  const node = (await children(t, folderId)).find((n) => n.name === FILE && n.parentId === folderId) ?? null;
+  if (!node?.blobId) return { node, body: {} };
+  const url = t.downloadUrl
+    .replace('{accountId}', encodeURIComponent(t.accountId))
+    .replace('{blobId}', encodeURIComponent(node.blobId))
+    .replace('{name}', FILE)
+    .replace('{type}', encodeURIComponent(TYPE));
+  const res = await apiFetch(pathOf(url));
+  if (!res.ok) throw new Error(`settings download failed (${res.status})`);
+  const parsed = (await res.json()) as unknown;
+  return {
+    node,
+    body: parsed && typeof parsed === 'object' && !Array.isArray(parsed) ? (parsed as Record<string, unknown>) : {},
+  };
+}
+
+/** The account's theme, or null when there is none to read (no file, no Files, a failure). */
+export async function loadAccountTheme(): Promise<{ palette: PaletteId | null; mode: Mode | null } | null> {
+  const t = target;
+  if (!t) return null;
+  try {
+    const { body } = await readFile(t, await findFolder(t));
+    const palette = isPaletteId(body.palette) ? body.palette : null;
+    const mode = body.mode === 'light' || body.mode === 'dark' || body.mode === 'system' ? body.mode : null;
+    if (!palette && !mode) return null;
+    return { palette, mode };
+  } catch {
+    // A settings file we can't read must never cost anyone the admin; the cache stands.
+    return null;
+  }
+}
+
+/** The old single-value `theme`, derived exactly as the webmail does (its lib/palette.ts). */
+function legacyTheme(palette: PaletteId, mode: Mode, prefersDark: boolean): 'system' | 'light' | 'dark' | 'ihasmail' {
+  const effective = mode === 'system' ? (prefersDark ? 'dark' : 'light') : mode;
+  if (palette === 'ihasmail' && effective === 'dark') return 'ihasmail';
+  if (palette === 'default' && mode === 'system') return 'system';
+  return effective;
+}
+
+async function write(t: Target, choice: Choice): Promise<void> {
+  let folderId = await findFolder(t);
+  if (!folderId) {
+    const created = await call<{ created?: Record<string, { id: string }> }>('FileNode/set', {
+      accountId: t.accountId,
+      create: { d: { parentId: null, name: APP_FOLDER, nodeType: 'directory' } },
+    });
+    folderId = created.created?.d?.id ?? null;
+    if (!folderId) throw new Error('could not create the settings folder');
+  }
+  const { node, body } = await readFile(t, folderId);
+  const prefersDark = window.matchMedia?.('(prefers-color-scheme: dark)').matches ?? false;
+  const stored = body.mode === 'light' || body.mode === 'dark' || body.mode === 'system' ? body.mode : null;
+  const mode = choice.mode ?? stored ?? choice.fallbackMode;
+  const next = { ...body, palette: choice.palette, mode, theme: legacyTheme(choice.palette, mode, prefersDark) };
+  const json = JSON.stringify(next, null, 2);
+  const blob = new Blob([json], { type: TYPE });
+  const up = await apiFetch(pathOf(t.uploadUrl.replace('{accountId}', encodeURIComponent(t.accountId))), {
+    method: 'POST',
+    headers: { 'Content-Type': TYPE },
+    body: blob,
+  });
+  if (!up.ok) throw new Error(`settings upload failed (${up.status})`);
+  const { blobId } = (await up.json()) as { blobId: string };
+  if (node) {
+    await call('FileNode/set', {
+      accountId: t.accountId,
+      update: { [node.id]: { blobId, type: TYPE, size: blob.size } },
+    });
+  } else {
+    await call('FileNode/set', {
+      accountId: t.accountId,
+      create: { s: { parentId: folderId, name: FILE, blobId, type: TYPE, nodeType: 'file' } },
+    });
+  }
+}
+
+/**
+ * Queue the theme for the account. `mode` is null for a palette-only change, which keeps the
+ * account's stored mode (a webmail "system" stays "system"); `fallbackMode` is used only when
+ * nothing is stored. Coalesces: the newest choice wins, one write after changes stop.
+ */
+export function queueAccountTheme(palette: PaletteId, mode: Mode | null, fallbackMode: Mode): void {
+  if (!target) return;
+  pending = { palette, mode: mode ?? pending?.mode ?? null, fallbackMode };
+  if (timer) clearTimeout(timer);
+  timer = setTimeout(() => {
+    timer = null;
+    const t = target;
+    const choice = pending;
+    pending = null;
+    if (!t || !choice) return;
+    // One write at a time, in order.
+    chain = chain.then(() => write(t, choice)).catch(() => undefined);
+  }, DEBOUNCE_MS);
+}
diff --git a/src/pages/AdminPanel.tsx b/src/pages/AdminPanel.tsx
index d0dc825..32ba5c2 100644
--- a/src/pages/AdminPanel.tsx
+++ b/src/pages/AdminPanel.tsx
@@ -13,6 +13,7 @@ import { useSchemaStore } from '@/stores/schemaStore';
 import { useAccountStore } from '@/stores/accountStore';
 import { useUIStore } from '@/stores/uiStore';
 import { fetchSession, fetchSchema, fetchAccountInfo } from '@/services/jmap/client';
+import { loadAccountTheme, setAccountSettingsTarget } from '@/lib/accountSettings';
 import { setLocale } from '@/i18n';
 import { TopBar } from '@/components/layout/TopBar';
 import { Sidebar } from '@/components/layout/Sidebar';
@@ -144,6 +145,11 @@ export default function AdminPanel() {
         if (cancelled) return;
         setSession(accounts, primaryAccountId, apiUrl, maxObjectsInGet, maxObjectsInSet);
         useAuthStore.getState().setUsername(typeof session.username === 'string' ? session.username : null);
+        // INBUXA: the theme lives with the account, shared with the webmail.
+        setAccountSettingsTarget(session);
+        void loadAccountTheme().then((stored) => {
+          if (stored && !cancelled) useUIStore.getState().applyAccountTheme(stored.palette, stored.mode);
+        });
 
         const [schemaData, accountData] = await Promise.all([fetchSchema(), fetchAccountInfo()]);
 
diff --git a/src/services/jmap/client.ts b/src/services/jmap/client.ts
index 9d98223..f69410d 100644
--- a/src/services/jmap/client.ts
+++ b/src/services/jmap/client.ts
@@ -1,5 +1,6 @@
 /*
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <hello@stalw.art>
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
  *
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
@@ -32,7 +33,11 @@ export function getAccountId(objectType: string): string {
   return activeAccountId;
 }
 
-export async function jmapRequest(methodCalls: JmapMethodCall[], signal?: AbortSignal): Promise<JmapMethodResponse[]> {
+export async function jmapRequest(
+  methodCalls: JmapMethodCall[],
+  signal?: AbortSignal,
+  extraUsing: string[] = [],
+): Promise<JmapMethodResponse[]> {
   const { apiUrl } = useAuthStore.getState();
   let path = apiUrl || '/jmap';
   if (path.startsWith('http://') || path.startsWith('https://')) {
@@ -48,7 +53,7 @@ export async function jmapRequest(methodCalls: JmapMethodCall[], signal?: AbortS
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify({
-      using: JMAP_USING,
+      using: [...JMAP_USING, ...extraUsing],
       methodCalls,
     }),
     signal,
diff --git a/src/stores/uiStore.ts b/src/stores/uiStore.ts
index 4be95d5..1e82221 100644
--- a/src/stores/uiStore.ts
+++ b/src/stores/uiStore.ts
@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
+import { queueAccountTheme } from '@/lib/accountSettings';
 import { applyPalette, DEFAULT_PALETTE, isPaletteId, type PaletteId } from '@/lib/palettes';
 import { create } from 'zustand';
 import { persist } from 'zustand/middleware';
@@ -23,6 +24,8 @@ interface UIState {
   toggleTheme: () => void;
   setTheme: (theme: Theme) => void;
   setPalette: (palette: PaletteId) => void;
+  /** INBUXA: take the theme stored with the account, without writing it back. */
+  applyAccountTheme: (palette: PaletteId | null, mode: 'system' | 'light' | 'dark' | null) => void;
   toggleSidebar: () => void;
   setSidebarOpen: (open: boolean) => void;
   toggleSidebarCollapsed: () => void;
@@ -51,11 +54,13 @@ export const useUIStore = create<UIState>()(
         const next = get().theme === 'light' ? 'dark' : 'light';
         applyThemeClass(next);
         set({ theme: next });
+        queueAccountTheme(get().palette, next, next);
       },
 
       setTheme: (theme) => {
         applyThemeClass(theme);
         set({ theme });
+        queueAccountTheme(get().palette, theme, theme);
       },
 
       toggleSidebar: () => {
@@ -69,6 +74,22 @@ export const useUIStore = create<UIState>()(
       setPalette: (palette) => {
         applyPalette(palette);
         set({ palette });
+        queueAccountTheme(palette, null, get().theme);
+      },
+
+      applyAccountTheme: (palette, mode) => {
+        const next: Partial<UIState> = {};
+        if (palette) {
+          applyPalette(palette);
+          next.palette = palette;
+        }
+        if (mode) {
+          const theme: Theme =
+            mode === 'system' ? (window.matchMedia?.('(prefers-color-scheme: dark)').matches ? 'dark' : 'light') : mode;
+          applyThemeClass(theme);
+          next.theme = theme;
+        }
+        set(next);
       },
 
       toggleSidebarCollapsed: () => {