diff --git a/packages/lib/services/e2ee/utils.test.ts b/packages/lib/services/e2ee/utils.test.ts
@@ -0,0 +1,42 @@
+import { afterAllCleanUp, setupDatabaseAndSynchronizer, switchClient, encryptionService } from '../../testing/test-utils';
+import MasterKey from '../../models/MasterKey';
+import { showMissingMasterKeyMessage } from './utils';
+import { localSyncInfo, setMasterKeyEnabled } from '../synchronizer/syncInfoUtils';
+
+describe('e2ee/utils', function() {
+
+	beforeEach(async (done) => {
+		await setupDatabaseAndSynchronizer(1);
+		await switchClient(1);
+		done();
+	});
+
+	afterAll(async () => {
+		await afterAllCleanUp();
+	});
+
+	it('should tell if the missing master key message should be shown', async () => {
+		const mk1 = await MasterKey.save(await encryptionService().generateMasterKey('111111'));
+		const mk2 = await MasterKey.save(await encryptionService().generateMasterKey('111111'));
+
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id])).toBe(true);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id, mk2.id])).toBe(true);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [])).toBe(false);
+
+		setMasterKeyEnabled(mk1.id, false);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id])).toBe(false);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id, mk2.id])).toBe(true);
+
+		setMasterKeyEnabled(mk2.id, false);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id, mk2.id])).toBe(false);
+
+		setMasterKeyEnabled(mk1.id, true);
+		setMasterKeyEnabled(mk2.id, true);
+		expect(showMissingMasterKeyMessage(localSyncInfo(), [mk1.id, mk2.id])).toBe(true);
+
+		const syncInfo = localSyncInfo();
+		syncInfo.masterKeys = [];
+		expect(showMissingMasterKeyMessage(syncInfo, [mk1.id, mk2.id])).toBe(false);
+	});
+
+});
diff --git a/packages/lib/services/e2ee/utils.ts b/packages/lib/services/e2ee/utils.ts
@@ -2,9 +2,9 @@ import Logger from '../../Logger';
 import BaseItem from '../../models/BaseItem';
 import MasterKey from '../../models/MasterKey';
 import Setting from '../../models/Setting';
-import { MasterKeyEntity } from '../database/types';
+import { MasterKeyEntity } from './types';
 import EncryptionService from '../EncryptionService';
-import { getActiveMasterKeyId, setEncryptionEnabled } from '../synchronizer/syncInfoUtils';
+import { getActiveMasterKeyId, masterKeyEnabled, setEncryptionEnabled, SyncInfo } from '../synchronizer/syncInfoUtils';
 
 const logger = Logger.create('e2ee/utils');
 
@@ -90,3 +90,16 @@ export async function loadMasterKeysFromSettings(service: EncryptionService) {
 
 	logger.info(`Loaded master keys: ${service.loadedMasterKeysCount()}`);
 }
+
+export function showMissingMasterKeyMessage(syncInfo: SyncInfo, notLoadedMasterKeys: string[]) {
+	if (!syncInfo.masterKeys.length) return false;
+
+	notLoadedMasterKeys = notLoadedMasterKeys.slice();
+
+	for (let i = notLoadedMasterKeys.length - 1; i >= 0; i--) {
+		const mk = syncInfo.masterKeys.find(mk => mk.id === notLoadedMasterKeys[i]);
+		if (!masterKeyEnabled(mk)) notLoadedMasterKeys.pop();
+	}
+
+	return !!notLoadedMasterKeys.length;
+}
diff --git a/packages/lib/services/synchronizer/syncInfoUtils.test.ts b/packages/lib/services/synchronizer/syncInfoUtils.test.ts
@@ -0,0 +1,37 @@
+import { afterAllCleanUp, setupDatabaseAndSynchronizer, switchClient, encryptionService } from '../../testing/test-utils';
+import MasterKey from '../../models/MasterKey';
+import { masterKeyEnabled, setMasterKeyEnabled } from './syncInfoUtils';
+
+describe('syncInfoUtils', function() {
+
+	beforeEach(async (done) => {
+		await setupDatabaseAndSynchronizer(1);
+		await switchClient(1);
+		done();
+	});
+
+	afterAll(async () => {
+		await afterAllCleanUp();
+	});
+
+	it('should enable or disable a master key', async () => {
+		const mk1 = await MasterKey.save(await encryptionService().generateMasterKey('111111'));
+		const mk2 = await MasterKey.save(await encryptionService().generateMasterKey('111111'));
+
+		setMasterKeyEnabled(mk2.id, false);
+
+		expect(masterKeyEnabled(await MasterKey.load(mk1.id))).toBe(true);
+		expect(masterKeyEnabled(await MasterKey.load(mk2.id))).toBe(false);
+
+		setMasterKeyEnabled(mk1.id, false);
+
+		expect(masterKeyEnabled(await MasterKey.load(mk1.id))).toBe(false);
+		expect(masterKeyEnabled(await MasterKey.load(mk2.id))).toBe(false);
+
+		setMasterKeyEnabled(mk1.id, true);
+
+		expect(masterKeyEnabled(await MasterKey.load(mk1.id))).toBe(true);
+		expect(masterKeyEnabled(await MasterKey.load(mk2.id))).toBe(false);
+	});
+
+});
diff --git a/packages/lib/services/synchronizer/syncInfoUtils.ts b/packages/lib/services/synchronizer/syncInfoUtils.ts
@@ -2,7 +2,7 @@ import { FileApi } from '../../file-api';
 import JoplinDatabase from '../../JoplinDatabase';
 import Setting from '../../models/Setting';
 import { State } from '../../reducer';
-import { MasterKeyEntity } from '../database/types';
+import { MasterKeyEntity } from '../e2ee/types';
 
 export interface SyncInfoValueBoolean {
 	value: boolean;
@@ -233,3 +233,24 @@ export function getActiveMasterKey(s: SyncInfo = null): MasterKeyEntity | null {
 	if (!s.activeMasterKeyId) return null;
 	return s.masterKeys.find(mk => mk.id === s.activeMasterKeyId);
 }
+
+export function setMasterKeyEnabled(mkId: string, enabled: boolean = true) {
+	const s = localSyncInfo();
+	const idx = s.masterKeys.findIndex(mk => mk.id === mkId);
+	if (idx < 0) throw new Error(`No such master key: ${mkId}`);
+
+	if (mkId === getActiveMasterKeyId() && !enabled) throw new Error('The active master key cannot be disabled');
+
+	s.masterKeys[idx] = {
+		...s.masterKeys[idx],
+		enabled: enabled ? 1 : 0,
+		updated_time: Date.now(),
+	};
+
+	saveLocalSyncInfo(s);
+}
+
+export function masterKeyEnabled(mk: MasterKeyEntity): boolean {
+	if ('enabled' in mk) return !!mk.enabled;
+	return true;
+}
diff --git a/packages/tools/generate-database-types.ts b/packages/tools/generate-database-types.ts
@@ -22,6 +22,7 @@ async function main() {
 			'main.notes_fts_segdir',
 			'main.notes_fts_docsize',
 			'main.notes_fts_stat',
+			'main.master_keys',
 		],
 	};