diff --git a/src/definition/AppStatus.ts b/src/definition/AppStatus.ts
index 3990ce4cc..30e843e06 100644
--- a/src/definition/AppStatus.ts
+++ b/src/definition/AppStatus.ts
@@ -51,6 +51,13 @@ export class AppStatusUtilsDef {
                 return false;
         }
     }
+
+    public isError(status: AppStatus): boolean {
+        return [
+            AppStatus.ERROR_DISABLED,
+            AppStatus.COMPILER_ERROR_DISABLED,
+        ].includes(status);
+    }
 }
 
 export const AppStatusUtils = new AppStatusUtilsDef();
diff --git a/src/definition/metadata/AppInterface.ts b/src/definition/metadata/AppInterface.ts
new file mode 100644
index 000000000..42083112b
--- /dev/null
+++ b/src/definition/metadata/AppInterface.ts
@@ -0,0 +1,36 @@
+export enum AppInterface {
+    // Messages
+    IPreMessageSentPrevent = 'IPreMessageSentPrevent',
+    IPreMessageSentExtend = 'IPreMessageSentExtend',
+    IPreMessageSentModify = 'IPreMessageSentModify',
+    IPostMessageSent = 'IPostMessageSent',
+    IPreMessageDeletePrevent = 'IPreMessageDeletePrevent',
+    IPostMessageDeleted = 'IPostMessageDeleted',
+    IPreMessageUpdatedPrevent = 'IPreMessageUpdatedPrevent',
+    IPreMessageUpdatedExtend = 'IPreMessageUpdatedExtend',
+    IPreMessageUpdatedModify = 'IPreMessageUpdatedModify',
+    IPostMessageUpdated = 'IPostMessageUpdated',
+    // Rooms
+    IPreRoomCreatePrevent = 'IPreRoomCreatePrevent',
+    IPreRoomCreateExtend = 'IPreRoomCreateExtend',
+    IPreRoomCreateModify = 'IPreRoomCreateModify',
+    IPostRoomCreate = 'IPostRoomCreate',
+    IPreRoomDeletePrevent = 'IPreRoomDeletePrevent',
+    IPostRoomDeleted = 'IPostRoomDeleted',
+    IPreRoomUserJoined = 'IPreRoomUserJoined',
+    IPostRoomUserJoined = 'IPostRoomUserJoined',
+    // External Components
+    IPostExternalComponentOpened = 'IPostExternalComponentOpened',
+    IPostExternalComponentClosed = 'IPostExternalComponentClosed',
+    // Blocks
+    IUIKitInteractionHandler = 'IUIKitInteractionHandler',
+    // Livechat
+    IPostLivechatRoomStarted = 'IPostLivechatRoomStarted',
+    IPostLivechatRoomClosed = 'IPostLivechatRoomClosed',
+    /**
+     * @deprecated please use the AppMethod.EXECUTE_POST_LIVECHAT_ROOM_CLOSED method
+     */
+    ILivechatRoomClosedHandler = 'ILivechatRoomClosedHandler',
+    IPostLivechatAgentAssigned = 'IPostLivechatAgentAssigned',
+    IPostLivechatAgentUnassigned = 'IPostLivechatAgentUnassigned',
+}
diff --git a/src/definition/metadata/IAppInfo.ts b/src/definition/metadata/IAppInfo.ts
index e48075951..ab8b26a64 100644
--- a/src/definition/metadata/IAppInfo.ts
+++ b/src/definition/metadata/IAppInfo.ts
@@ -1,3 +1,4 @@
+import { AppInterface } from './AppInterface';
 import { IAppAuthorInfo } from './IAppAuthorInfo';
 
 export interface IAppInfo {
@@ -12,4 +13,5 @@ export interface IAppInfo {
     iconFile: string;
     /** Base64 string of the App's icon. */
     iconFileContent?: string;
+    essentials?: [AppInterface];
 }
diff --git a/src/definition/metadata/index.ts b/src/definition/metadata/index.ts
index f0c7e95b7..5894b2eca 100644
--- a/src/definition/metadata/index.ts
+++ b/src/definition/metadata/index.ts
@@ -3,6 +3,8 @@ import { IAppAuthorInfo } from './IAppAuthorInfo';
 import { IAppInfo } from './IAppInfo';
 import { RocketChatAssociationModel, RocketChatAssociationRecord } from './RocketChatAssociations';
 
+export * from './AppInterface';
+
 export {
     AppMethod,
     IAppAuthorInfo,
diff --git a/src/server/AppManager.ts b/src/server/AppManager.ts
index d8b84882c..f9135e983 100644
--- a/src/server/AppManager.ts
+++ b/src/server/AppManager.ts
@@ -222,9 +222,11 @@ export class AppManager {
 
         // Now let's enable the apps which were once enabled
         // but are not currently disabled.
-        for (const rl of this.apps.values()) {
-            if (!AppStatusUtils.isDisabled(rl.getStatus()) && AppStatusUtils.isEnabled(rl.getPreviousStatus())) {
-                await this.enableApp(items.get(rl.getID()), rl, true, rl.getPreviousStatus() === AppStatus.MANUALLY_ENABLED).catch(console.error);
+        for (const app of this.apps.values()) {
+            if (!AppStatusUtils.isDisabled(app.getStatus()) && AppStatusUtils.isEnabled(app.getPreviousStatus())) {
+                await this.enableApp(items.get(app.getID()), app, true, app.getPreviousStatus() === AppStatus.MANUALLY_ENABLED).catch(console.error);
+            } else if (!AppStatusUtils.isError(app.getStatus())) {
+                this.listenerManager.lockEssentialEvents(app);
             }
         }
 
@@ -239,21 +241,18 @@ export class AppManager {
             return;
         }
 
-        for (const rl of this.apps.values()) {
-            if (AppStatusUtils.isDisabled(rl.getStatus())) {
-                continue;
-            }
-
-            if (rl.getStatus() === AppStatus.INITIALIZED) {
-                this.listenerManager.unregisterListeners(rl);
-                this.commandManager.unregisterCommands(rl.getID());
-                this.externalComponentManager.unregisterExternalComponents(rl.getID());
-                this.apiManager.unregisterApis(rl.getID());
-                this.accessorManager.purifyApp(rl.getID());
-                continue;
+        for (const app of this.apps.values()) {
+            if (app.getStatus() === AppStatus.INITIALIZED) {
+                this.listenerManager.unregisterListeners(app);
+                this.commandManager.unregisterCommands(app.getID());
+                this.externalComponentManager.unregisterExternalComponents(app.getID());
+                this.apiManager.unregisterApis(app.getID());
+                this.accessorManager.purifyApp(app.getID());
+            } else if (!AppStatusUtils.isDisabled(app.getStatus())) {
+                await this.disable(app.getID(), isManual ? AppStatus.MANUALLY_DISABLED : AppStatus.DISABLED);
             }
 
-            await this.disable(rl.getID(), isManual ? AppStatus.MANUALLY_DISABLED : AppStatus.DISABLED);
+            this.listenerManager.releaseEssentialEvents(app);
         }
 
         // Remove all the apps from the system now that we have unloaded everything
@@ -350,33 +349,34 @@ export class AppManager {
             throw new Error('Invalid disabled status');
         }
 
-        const rl = this.apps.get(id);
+        const app = this.apps.get(id);
 
-        if (!rl) {
+        if (!app) {
             throw new Error(`No App by the id "${id}" exists.`);
         }
 
-        if (AppStatusUtils.isEnabled(rl.getStatus())) {
-            await rl.call(AppMethod.ONDISABLE, this.accessorManager.getConfigurationModify(rl.getID()))
+        if (AppStatusUtils.isEnabled(app.getStatus())) {
+            await app.call(AppMethod.ONDISABLE, this.accessorManager.getConfigurationModify(app.getID()))
                 .catch((e) => console.warn('Error while disabling:', e));
         }
 
-        this.listenerManager.unregisterListeners(rl);
-        this.commandManager.unregisterCommands(rl.getID());
-        this.externalComponentManager.unregisterExternalComponents(rl.getID());
-        this.apiManager.unregisterApis(rl.getID());
-        this.accessorManager.purifyApp(rl.getID());
+        this.listenerManager.unregisterListeners(app);
+        this.listenerManager.lockEssentialEvents(app);
+        this.commandManager.unregisterCommands(app.getID());
+        this.externalComponentManager.unregisterExternalComponents(app.getID());
+        this.apiManager.unregisterApis(app.getID());
+        this.accessorManager.purifyApp(app.getID());
 
-        await rl.setStatus(status, silent);
+        await app.setStatus(status, silent);
 
         const storageItem = await this.storage.retrieveOne(id);
 
-        rl.getStorageItem().marketplaceInfo = storageItem.marketplaceInfo;
-        await rl.validateLicense().catch();
+        app.getStorageItem().marketplaceInfo = storageItem.marketplaceInfo;
+        await app.validateLicense().catch();
 
         // This is async, but we don't care since it only updates in the database
         // and it should not mutate any properties we care about
-        storageItem.status = rl.getStatus();
+        storageItem.status = app.getStatus();
         await this.storage.update(storageItem).catch();
 
         return true;
@@ -462,6 +462,7 @@ export class AppManager {
         }
 
         this.listenerManager.unregisterListeners(app);
+        this.listenerManager.releaseEssentialEvents(app);
         this.commandManager.unregisterCommands(app.getID());
         this.externalComponentManager.purgeExternalComponents(app.getID());
         this.apiManager.unregisterApis(app.getID());
@@ -796,10 +797,12 @@ export class AppManager {
             this.externalComponentManager.registerExternalComponents(app.getID());
             this.apiManager.registerApis(app.getID());
             this.listenerManager.registerListeners(app);
+            this.listenerManager.releaseEssentialEvents(app);
         } else {
             this.commandManager.unregisterCommands(app.getID());
             this.externalComponentManager.unregisterExternalComponents(app.getID());
             this.apiManager.unregisterApis(app.getID());
+            this.listenerManager.lockEssentialEvents(app);
         }
 
         if (saveToDb) {
diff --git a/src/server/ProxiedApp.ts b/src/server/ProxiedApp.ts
index 85e03095c..6d210bc85 100644
--- a/src/server/ProxiedApp.ts
+++ b/src/server/ProxiedApp.ts
@@ -154,6 +154,10 @@ export class ProxiedApp implements IApp {
         return this.app.getAccessors();
     }
 
+    public getEssentials(): IAppInfo['essentials'] {
+        return this.getInfo().essentials;
+    }
+
     public getLatestLicenseValidationResult(): AppLicenseValidationResult {
         return this.latestLicenseValidationResult;
     }
diff --git a/src/server/bridges/IListenerBridge.ts b/src/server/bridges/IListenerBridge.ts
index fbf103678..cce42858e 100644
--- a/src/server/bridges/IListenerBridge.ts
+++ b/src/server/bridges/IListenerBridge.ts
@@ -1,7 +1,7 @@
 import { IMessage } from '../../definition/messages';
+import { AppInterface } from '../../definition/metadata';
 import { IRoom } from '../../definition/rooms';
 import { IUIKitIncomingInteraction } from '../../definition/uikit';
-import { AppInterface } from '../compiler';
 
 export interface IListenerBridge {
     messageEvent(int: AppInterface, message: IMessage): Promise<void | boolean | IMessage>;
diff --git a/src/server/compiler/AppImplements.ts b/src/server/compiler/AppImplements.ts
index 1894ab38f..459138a33 100644
--- a/src/server/compiler/AppImplements.ts
+++ b/src/server/compiler/AppImplements.ts
@@ -1,42 +1,6 @@
+import { AppInterface } from '../../definition/metadata/AppInterface';
 import { Utilities } from '../misc/Utilities';
 
-export enum AppInterface {
-    // Messages
-    IPreMessageSentPrevent = 'IPreMessageSentPrevent',
-    IPreMessageSentExtend = 'IPreMessageSentExtend',
-    IPreMessageSentModify = 'IPreMessageSentModify',
-    IPostMessageSent = 'IPostMessageSent',
-    IPreMessageDeletePrevent = 'IPreMessageDeletePrevent',
-    IPostMessageDeleted = 'IPostMessageDeleted',
-    IPreMessageUpdatedPrevent = 'IPreMessageUpdatedPrevent',
-    IPreMessageUpdatedExtend = 'IPreMessageUpdatedExtend',
-    IPreMessageUpdatedModify = 'IPreMessageUpdatedModify',
-    IPostMessageUpdated = 'IPostMessageUpdated',
-    // Rooms
-    IPreRoomCreatePrevent = 'IPreRoomCreatePrevent',
-    IPreRoomCreateExtend = 'IPreRoomCreateExtend',
-    IPreRoomCreateModify = 'IPreRoomCreateModify',
-    IPostRoomCreate = 'IPostRoomCreate',
-    IPreRoomDeletePrevent = 'IPreRoomDeletePrevent',
-    IPostRoomDeleted = 'IPostRoomDeleted',
-    IPreRoomUserJoined = 'IPreRoomUserJoined',
-    IPostRoomUserJoined = 'IPostRoomUserJoined',
-    // External Components
-    IPostExternalComponentOpened = 'IPostExternalComponentOpened',
-    IPostExternalComponentClosed = 'IPostExternalComponentClosed',
-    // Blocks
-    IUIKitInteractionHandler = 'IUIKitInteractionHandler',
-    // Livechat
-    IPostLivechatRoomStarted = 'IPostLivechatRoomStarted',
-    IPostLivechatRoomClosed = 'IPostLivechatRoomClosed',
-    /**
-     * @deprecated please use the AppMethod.EXECUTE_POST_LIVECHAT_ROOM_CLOSED method
-     */
-    ILivechatRoomClosedHandler = 'ILivechatRoomClosedHandler',
-    IPostLivechatAgentAssigned = 'IPostLivechatAgentAssigned',
-    IPostLivechatAgentUnassigned = 'IPostLivechatAgentUnassigned',
-}
-
 export class AppImplements {
     private implemented: { [key: string]: boolean };
 
diff --git a/src/server/compiler/index.ts b/src/server/compiler/index.ts
index 7e72478ab..4bd13fe1a 100644
--- a/src/server/compiler/index.ts
+++ b/src/server/compiler/index.ts
@@ -1,6 +1,6 @@
 import { AppCompiler } from './AppCompiler';
 import { AppFabricationFulfillment } from './AppFabricationFulfillment';
-import { AppImplements, AppInterface } from './AppImplements';
+import { AppImplements } from './AppImplements';
 import { AppPackageParser } from './AppPackageParser';
 import { ICompilerError } from './ICompilerError';
 import { ICompilerFile } from './ICompilerFile';
@@ -11,7 +11,6 @@ export {
     AppCompiler,
     AppFabricationFulfillment,
     AppImplements,
-    AppInterface,
     AppPackageParser,
     ICompilerFile,
     ICompilerError,
diff --git a/src/server/managers/AppListenerManager.ts b/src/server/managers/AppListenerManager.ts
index 2d886a95f..a2014e05e 100644
--- a/src/server/managers/AppListenerManager.ts
+++ b/src/server/managers/AppListenerManager.ts
@@ -1,7 +1,8 @@
+import { AppsEngineException } from '../../definition/exceptions';
 import { IExternalComponent } from '../../definition/externalComponent';
 import { ILivechatEventContext, ILivechatRoom } from '../../definition/livechat';
 import { IMessage } from '../../definition/messages';
-import { AppMethod } from '../../definition/metadata';
+import { AppInterface, AppMethod } from '../../definition/metadata';
 import { IRoom, IRoomUserJoinedContext } from '../../definition/rooms';
 import { IUIKitIncomingInteraction, IUIKitResponse, IUIKitView, UIKitIncomingInteractionType } from '../../definition/uikit';
 import {
@@ -16,32 +17,46 @@ import {
 import { IUser } from '../../definition/users';
 import { MessageBuilder, MessageExtender, RoomBuilder, RoomExtender } from '../accessors';
 import { AppManager } from '../AppManager';
-import { AppInterface } from '../compiler';
 import { Message } from '../messages/Message';
 import { Utilities } from '../misc/Utilities';
 import { ProxiedApp } from '../ProxiedApp';
 import { Room } from '../rooms/Room';
 import { AppAccessorManager } from './AppAccessorManager';
 
+export class EssentialAppDisabledException extends AppsEngineException {}
+
 export class AppListenerManager {
     private am: AppAccessorManager;
     private listeners: Map<string, Array<string>>;
+    /**
+     * Locked events are those who are listed in an app's
+     * "essentials" list but the app is disabled.
+     *
+     * They will throw a EssentialAppDisabledException upon call
+     */
+    private lockedEvents: Map<string, Set<string>>;
 
     constructor(private readonly manager: AppManager) {
         this.am = manager.getAccessorManager();
         this.listeners = new Map<string, Array<string>>();
+        this.lockedEvents = new Map<string, Set<string>>();
 
-        Object.keys(AppInterface).forEach((intt) => this.listeners.set(intt, new Array<string>()));
+        Object.keys(AppInterface).forEach((intt) => {
+            this.listeners.set(intt, new Array<string>());
+            this.lockedEvents.set(intt, new Set<string>());
+        });
     }
 
     public registerListeners(app: ProxiedApp): void {
         this.unregisterListeners(app);
-        const impleList = app.getImplementationList();
-        for (const int in app.getImplementationList()) {
-            if (impleList[int]) {
-                this.listeners.get(int).push(app.getID());
+
+        Object.entries(app.getImplementationList()).forEach(([event, isImplemented]) => {
+            if (!isImplemented) {
+                return;
             }
-        }
+
+            this.listeners.get(event).push(app.getID());
+        });
     }
 
     public unregisterListeners(app: ProxiedApp): void {
@@ -53,6 +68,38 @@ export class AppListenerManager {
         });
     }
 
+    public releaseEssentialEvents(app: ProxiedApp): void {
+        if (!app.getEssentials()) {
+            return;
+        }
+
+        app.getEssentials().forEach((event) => {
+            const lockedEvent = this.lockedEvents.get(event);
+
+            if (!lockedEvent) {
+                return;
+            }
+
+            lockedEvent.delete(app.getID());
+        });
+    }
+
+    public lockEssentialEvents(app: ProxiedApp): void {
+        if (!app.getEssentials()) {
+            return;
+        }
+
+        app.getEssentials().forEach((event) => {
+            const lockedEvent = this.lockedEvents.get(event);
+
+            if (!lockedEvent) {
+                return;
+            }
+
+            lockedEvent.add(app.getID());
+        });
+    }
+
     public getListeners(int: AppInterface): Array<ProxiedApp> {
         const results = new Array<ProxiedApp>();
 
@@ -63,8 +110,18 @@ export class AppListenerManager {
         return results;
     }
 
+    public isEventBlocked(event: AppInterface): boolean {
+        const lockedEventList = this.lockedEvents.get(event);
+
+        return !!(lockedEventList && lockedEventList.size);
+    }
+
     // tslint:disable-next-line
     public async executeListener(int: AppInterface, data: IMessage | IRoom | IUser | ILivechatRoom | IUIKitIncomingInteraction | IExternalComponent | ILivechatEventContext | IRoomUserJoinedContext): Promise<void | boolean | IMessage | IRoom | IUser | IUIKitResponse | ILivechatRoom> {
+        if (this.isEventBlocked(int)) {
+            throw new EssentialAppDisabledException('There is one or more apps that are essential to this event but are disabled');
+        }
+
         switch (int) {
             // Messages
             case AppInterface.IPreMessageSentPrevent:
@@ -137,7 +194,7 @@ export class AppListenerManager {
                 this.executePostLivechatAgentUnassigned(data as ILivechatEventContext);
                 return;
             default:
-                console.warn('Unimplemented (or invalid) AppInterface was just tried to execute.');
+                console.warn('An invalid listener was called');
                 return;
         }
     }
diff --git a/tests/server/compiler/AppFabricationFulfillment.spec.ts b/tests/server/compiler/AppFabricationFulfillment.spec.ts
index a77a11c74..ea55b783b 100644
--- a/tests/server/compiler/AppFabricationFulfillment.spec.ts
+++ b/tests/server/compiler/AppFabricationFulfillment.spec.ts
@@ -1,10 +1,9 @@
 import { Expect, Test } from 'alsatian';
 import { App } from '../../../src/definition/App';
 import { AppStatus } from '../../../src/definition/AppStatus';
-import { IAppInfo } from '../../../src/definition/metadata';
-
+import { AppInterface, IAppInfo } from '../../../src/definition/metadata';
 import { AppManager } from '../../../src/server/AppManager';
-import { AppFabricationFulfillment, AppInterface, ICompilerError } from '../../../src/server/compiler';
+import { AppFabricationFulfillment, ICompilerError } from '../../../src/server/compiler';
 import { ProxiedApp } from '../../../src/server/ProxiedApp';
 import { IAppStorageItem } from '../../../src/server/storage';
 
diff --git a/tests/server/compiler/AppImplements.spec.ts b/tests/server/compiler/AppImplements.spec.ts
index bca227534..ee2e55647 100644
--- a/tests/server/compiler/AppImplements.spec.ts
+++ b/tests/server/compiler/AppImplements.spec.ts
@@ -1,6 +1,6 @@
 import { Expect, Test } from 'alsatian';
-
-import { AppImplements, AppInterface } from '../../../src/server/compiler';
+import { AppInterface } from '../../../src/definition/metadata';
+import { AppImplements } from '../../../src/server/compiler';
 
 export class AppImplementsTestFixture {
     @Test()
diff --git a/tests/server/managers/AppListenerManager.spec.ts b/tests/server/managers/AppListenerManager.spec.ts
index 33e75e88c..45e23f76c 100644
--- a/tests/server/managers/AppListenerManager.spec.ts
+++ b/tests/server/managers/AppListenerManager.spec.ts
@@ -1,6 +1,6 @@
 import { Expect, SetupFixture, Test } from 'alsatian';
+import { AppInterface } from '../../../src/definition/metadata';
 import { AppManager } from '../../../src/server/AppManager';
-import { AppInterface } from '../../../src/server/compiler';
 import { AppListenerManager } from '../../../src/server/managers';
 import { ProxiedApp } from '../../../src/server/ProxiedApp';