diff --git a/android/app/src/main/AndroidManifest.xml b/android/app/src/main/AndroidManifest.xml
index 71324ad2..dc980690 100644
--- a/android/app/src/main/AndroidManifest.xml
+++ b/android/app/src/main/AndroidManifest.xml
@@ -47,6 +47,13 @@
         <category android:name="android.intent.category.BROWSABLE"/>
         <data android:scheme="bulwarkmail"/>
       </intent-filter>
+      <!-- Browser sign-in callback of the client the app registers at Stalwart 1.0 (org.bulwarkmail.mobile:/auth/callback). -->
+      <intent-filter>
+        <action android:name="android.intent.action.VIEW"/>
+        <category android:name="android.intent.category.DEFAULT"/>
+        <category android:name="android.intent.category.BROWSABLE"/>
+        <data android:scheme="org.bulwarkmail.mobile"/>
+      </intent-filter>
       <intent-filter>
         <action android:name="android.intent.action.VIEW"/>
         <action android:name="android.intent.action.SENDTO"/>
diff --git a/app.config.js b/app.config.js
index 2e8dbadf..bf40cb11 100644
--- a/app.config.js
+++ b/app.config.js
@@ -35,8 +35,10 @@ module.exports = {
     slug: 'bulwark-mobile',
     // mailto: lets Android/iOS offer the app for mail links in other apps;
     // bulwarkmail: is the webmail's sign-in link (bulwarkmail://pair?...).
+    // org.bulwarkmail.mobile: is where Stalwart 1.0 sends the browser sign-in
+    // back: it registers public clients only with a scheme that has a dot.
     // Android's manifest is maintained by hand and lists the same schemes.
-    scheme: ['bulwarkmobile', 'bulwarkmail', 'mailto'],
+    scheme: ['bulwarkmobile', 'bulwarkmail', 'mailto', 'org.bulwarkmail.mobile'],
     version: VERSION,
     orientation: 'default',
     icon: './assets/icon.png',
diff --git a/src/lib/__tests__/oauth-native.test.ts b/src/lib/__tests__/oauth-native.test.ts
index 3f0b5bde..8c26ef6f 100644
--- a/src/lib/__tests__/oauth-native.test.ts
+++ b/src/lib/__tests__/oauth-native.test.ts
@@ -5,8 +5,10 @@ vi.mock('../client-cert', () => ({
   secureFetch: vi.fn(),
 }));
 
-import { loginWithPkce, type OAuthMetadata } from '../oauth-native';
+import { secureFetch } from '../client-cert';
+import { loginWithPkce, pkceScopes, type OAuthMetadata } from '../oauth-native';
 import { HandoffCancelledError } from '../oauth';
+import { REGISTERED_REDIRECT_URI, resetLoginClients } from '../totp-login';
 
 const mockOpenAuthSession = WebBrowser.openAuthSessionAsync as ReturnType<typeof vi.fn>;
 
@@ -61,3 +63,62 @@ describe('loginWithPkce', () => {
     expect(params.get('prompt')).toBe('select_account');
   });
 });
+
+describe('loginWithPkce on Stalwart', () => {
+  const fetchMock = secureFetch as unknown as ReturnType<typeof vi.fn>;
+  const stalwart: OAuthMetadata = {
+    ...metadata,
+    authorization_endpoint: 'https://mail.example.com/login',
+    scopes_supported: [
+      'openid',
+      'offline_access',
+      'urn:ietf:params:oauth:scope:mail',
+      'urn:ietf:params:oauth:scope:contacts',
+      'urn:ietf:params:oauth:scope:calendars',
+      'urn:ietf:params:oauth:scope:files',
+    ],
+  };
+  const answer = (body: unknown, status = 200) =>
+    new Response(JSON.stringify(body), { status, headers: { 'Content-Type': 'application/json' } });
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    resetLoginClients();
+  });
+
+  it('signs in on 1.0 with a client it registers, on a redirect 1.0 accepts', async () => {
+    fetchMock.mockImplementation(async (url: string) => {
+      if (url.includes('/api/auth/client')) return answer({ error: 'invalid_client', description: 'Unknown client id' });
+      if (url.endsWith('/auth/register')) return answer({ client_id: 'swc1.abc' }, 201);
+      return answer({}, 404);
+    });
+    const { params, redirectUri } = await openedSession(stalwart);
+
+    expect(params.get('client_id')).toBe('swc1.abc');
+    expect(params.get('redirect_uri')).toBe(REGISTERED_REDIRECT_URI);
+    expect(redirectUri).toBe(REGISTERED_REDIRECT_URI);
+  });
+
+  it('keeps the webmail client and the app scheme on 0.16', async () => {
+    fetchMock.mockImplementation(async () => answer({ status: 404 }, 404));
+    const { params, redirectUri } = await openedSession(stalwart);
+
+    expect(params.get('client_id')).toBe('bulwark-webmail');
+    expect(redirectUri).toBe('bulwarkmobile://auth/callback');
+  });
+
+  it("asks for Stalwart's data scopes and none it doesn't list", async () => {
+    fetchMock.mockImplementation(async () => answer({ status: 404 }, 404));
+    const { params } = await openedSession(stalwart);
+    const scopes = params.get('scope')!.split(' ');
+
+    expect(scopes).toEqual(expect.arrayContaining(['openid', 'offline_access', 'urn:ietf:params:oauth:scope:mail', 'urn:ietf:params:oauth:scope:files']));
+    expect(scopes).not.toContain('email');
+    expect(scopes).not.toContain('profile');
+  });
+
+  it('asks another identity provider for the usual OpenID scopes', () => {
+    expect(pkceScopes({ ...metadata, scopes_supported: ['openid', 'email', 'profile', 'offline_access', 'groups'] }))
+      .toBe('openid email profile offline_access');
+  });
+});
diff --git a/src/lib/oauth-native.ts b/src/lib/oauth-native.ts
index 7f7d09de..f5df3754 100644
--- a/src/lib/oauth-native.ts
+++ b/src/lib/oauth-native.ts
@@ -13,7 +13,12 @@
 import * as WebBrowser from 'expo-web-browser';
 import { secureFetch } from './client-cert';
 import { HANDOFF_REDIRECT_URI, HandoffError, HandoffCancelledError, type OAuthTokens } from './oauth';
-import { generateCodeChallenge, generateCodeVerifier, DEFAULT_CLIENT_ID } from './totp-login';
+import {
+  generateCodeChallenge,
+  generateCodeVerifier,
+  resolveLoginClient,
+  DEFAULT_CLIENT_ID,
+} from './totp-login';
 import { randomHex } from './random';
 
 export interface OAuthMetadata {
@@ -119,6 +124,45 @@ function addAccountPrompt(metadata: OAuthMetadata): string {
   return 'select_account';
 }
 
+const DATA_SCOPE_PREFIX = 'urn:ietf:params:oauth:scope:';
+
+/**
+ * Scopes to ask for (webmail lib/oauth/scopes.ts). A provider that
+ * advertises OAuth data scopes is Stalwart: 1.0 gives a client it doesn't
+ * treat as first-party only what these name, and refuses a scope it doesn't
+ * list (`email`, `profile`) with `invalid_scope`. For such a provider the
+ * scopes it doesn't list are dropped and every data scope it lists is added;
+ * any other provider gets the usual OIDC set.
+ */
+export function pkceScopes(metadata: OAuthMetadata): string {
+  const wanted = ['openid', 'email', 'profile', 'offline_access'];
+  const supported = metadata.scopes_supported;
+  if (!supported?.length) return wanted.join(' ');
+  const kept = wanted.filter((s) => supported.includes(s));
+  const data = supported.filter((s) => typeof s === 'string' && s.startsWith(DATA_SCOPE_PREFIX));
+  if (data.length) return [...new Set([...kept, ...data])].join(' ');
+  return kept.join(' ') || supported.join(' ');
+}
+
+/**
+ * The client the browser sign-in uses. When the server is its own
+ * authorization server (Stalwart), the same check as the password sign-in
+ * decides: 0.16 takes `bulwark-webmail` on `bulwarkmobile://`, 1.0 knows no
+ * such client and gets one the app registers. An external identity provider
+ * keeps the webmail's client id.
+ */
+async function pkceClient(serverUrl: string, metadata: OAuthMetadata): Promise<{ clientId: string; redirectUri: string }> {
+  if (sameHost(metadata.authorization_endpoint, serverUrl) && sameHost(metadata.token_endpoint, serverUrl)) {
+    try {
+      return await resolveLoginClient(serverUrl);
+    } catch {
+      // A refused registration or a redirect away: the browser shows what
+      // the server says about the default client.
+    }
+  }
+  return { clientId: DEFAULT_CLIENT_ID, redirectUri: HANDOFF_REDIRECT_URI };
+}
+
 /**
  * Run the authorization-code + PKCE flow in the system browser. Throws
  * `HandoffCancelledError` when the user closes the browser. With `addAccount`
@@ -130,15 +174,14 @@ export async function loginWithPkce(
   metadata: OAuthMetadata,
   opts?: { clientId?: string; scopes?: string; redirectUri?: string; addAccount?: boolean },
 ): Promise<OAuthTokens> {
-  const clientId = opts?.clientId ?? DEFAULT_CLIENT_ID;
-  const redirectUri = opts?.redirectUri ?? HANDOFF_REDIRECT_URI;
+  const client = opts?.clientId
+    ? { clientId: opts.clientId, redirectUri: opts.redirectUri ?? HANDOFF_REDIRECT_URI }
+    : await pkceClient(serverUrl, metadata);
+  const { clientId, redirectUri } = client;
   const verifier = generateCodeVerifier();
   const challenge = generateCodeChallenge(verifier);
   const state = randomHex(16);
-  const scope = opts?.scopes
-    ?? (metadata.scopes_supported?.length
-      ? ['openid', 'email', 'profile', 'offline_access'].filter((s) => metadata.scopes_supported!.includes(s)).join(' ') || metadata.scopes_supported.join(' ')
-      : 'openid email profile offline_access');
+  const scope = opts?.scopes ?? pkceScopes(metadata);
 
   const params = new URLSearchParams({
     response_type: 'code',