diff --git a/lib/shared/messages/add-members-message-spec.js b/lib/shared/messages/add-members-message-spec.js
--- a/lib/shared/messages/add-members-message-spec.js
+++ b/lib/shared/messages/add-members-message-spec.js
@@ -166,5 +166,7 @@
     return rawMessageInfo.addedUserIDs;
   },
 
+  canBeSidebarSource: true,
+
   validator: rawAddMembersMessageInfoValidator,
 });
diff --git a/lib/shared/messages/change-role-message-spec.js b/lib/shared/messages/change-role-message-spec.js
--- a/lib/shared/messages/change-role-message-spec.js
+++ b/lib/shared/messages/change-role-message-spec.js
@@ -236,5 +236,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawChangeRoleMessageInfoValidator,
 });
diff --git a/lib/shared/messages/change-settings-message-spec.js b/lib/shared/messages/change-settings-message-spec.js
--- a/lib/shared/messages/change-settings-message-spec.js
+++ b/lib/shared/messages/change-settings-message-spec.js
@@ -182,5 +182,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawChangeSettingsMessageInfoValidator,
 });
diff --git a/lib/shared/messages/create-entry-message-spec.js b/lib/shared/messages/create-entry-message-spec.js
--- a/lib/shared/messages/create-entry-message-spec.js
+++ b/lib/shared/messages/create-entry-message-spec.js
@@ -121,5 +121,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawCreateEntryMessageInfoValidator,
 });
diff --git a/lib/shared/messages/create-sidebar-message-spec.js b/lib/shared/messages/create-sidebar-message-spec.js
--- a/lib/shared/messages/create-sidebar-message-spec.js
+++ b/lib/shared/messages/create-sidebar-message-spec.js
@@ -229,5 +229,7 @@
     return [parentThreadID];
   },
 
+  canBeSidebarSource: true,
+
   validator: rawCreateSidebarMessageInfoValidator,
 });
diff --git a/lib/shared/messages/create-sub-thread-message-spec.js b/lib/shared/messages/create-sub-thread-message-spec.js
--- a/lib/shared/messages/create-sub-thread-message-spec.js
+++ b/lib/shared/messages/create-sub-thread-message-spec.js
@@ -163,5 +163,7 @@
     return [rawMessageInfo.childThreadID];
   },
 
+  canBeSidebarSource: true,
+
   validator: rawCreateSubthreadMessageInfoValidator,
 });
diff --git a/lib/shared/messages/create-thread-message-spec.js b/lib/shared/messages/create-thread-message-spec.js
--- a/lib/shared/messages/create-thread-message-spec.js
+++ b/lib/shared/messages/create-thread-message-spec.js
@@ -202,5 +202,7 @@
     return parentThreadID ? [parentThreadID] : [];
   },
 
+  canBeSidebarSource: true,
+
   validator: rawCreateThreadMessageInfoValidator,
 });
diff --git a/lib/shared/messages/delete-entry-message-spec.js b/lib/shared/messages/delete-entry-message-spec.js
--- a/lib/shared/messages/delete-entry-message-spec.js
+++ b/lib/shared/messages/delete-entry-message-spec.js
@@ -136,5 +136,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawDeleteEntryMessageInfoValidator,
 });
diff --git a/lib/shared/messages/edit-entry-message-spec.js b/lib/shared/messages/edit-entry-message-spec.js
--- a/lib/shared/messages/edit-entry-message-spec.js
+++ b/lib/shared/messages/edit-entry-message-spec.js
@@ -121,5 +121,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawEditEntryMessageInfoValidator,
 });
diff --git a/lib/shared/messages/edit-message-spec.js b/lib/shared/messages/edit-message-spec.js
--- a/lib/shared/messages/edit-message-spec.js
+++ b/lib/shared/messages/edit-message-spec.js
@@ -8,7 +8,7 @@
   assertMessageType,
   messageTypes,
 } from '../../types/message-types-enum.js';
-import { type ClientDBMessageInfo } from '../../types/message-types.js';
+import type { ClientDBMessageInfo } from '../../types/message-types.js';
 import {
   type EditMessageData,
   type RawEditMessageInfo,
@@ -140,5 +140,7 @@
     return unwrapped;
   },
 
+  canBeSidebarSource: false,
+
   validator: rawEditMessageInfoValidator,
 });
diff --git a/lib/shared/messages/join-thread-message-spec.js b/lib/shared/messages/join-thread-message-spec.js
--- a/lib/shared/messages/join-thread-message-spec.js
+++ b/lib/shared/messages/join-thread-message-spec.js
@@ -119,5 +119,7 @@
     return joinResult(rawMessageInfo.type, rawMessageInfo.threadID);
   },
 
+  canBeSidebarSource: true,
+
   validator: rawJoinThreadMessageInfoValidator,
 });
diff --git a/lib/shared/messages/leave-thread-message-spec.js b/lib/shared/messages/leave-thread-message-spec.js
--- a/lib/shared/messages/leave-thread-message-spec.js
+++ b/lib/shared/messages/leave-thread-message-spec.js
@@ -119,5 +119,7 @@
     return joinResult(rawMessageInfo.type, rawMessageInfo.threadID);
   },
 
+  canBeSidebarSource: true,
+
   validator: rawLeaveThreadMessageInfoValidator,
 });
diff --git a/lib/shared/messages/message-spec.js b/lib/shared/messages/message-spec.js
--- a/lib/shared/messages/message-spec.js
+++ b/lib/shared/messages/message-spec.js
@@ -113,6 +113,7 @@
   +startsThread?: boolean,
   +threadIDs?: (rawMessageInfo: RawInfo) => $ReadOnlyArray<string>,
   +includedInRepliesCount?: boolean,
+  +canBeSidebarSource: boolean,
   +useCreationSideEffectsFunc?: () => CreationSideEffectsFunc<RawInfo>,
   +validator: TType<RawInfo>,
 };
diff --git a/lib/shared/messages/multimedia-message-spec.js b/lib/shared/messages/multimedia-message-spec.js
--- a/lib/shared/messages/multimedia-message-spec.js
+++ b/lib/shared/messages/multimedia-message-spec.js
@@ -351,6 +351,8 @@
 
   includedInRepliesCount: true,
 
+  canBeSidebarSource: true,
+
   validator: rawMultimediaMessageInfoValidator,
 });
 
diff --git a/lib/shared/messages/reaction-message-spec.js b/lib/shared/messages/reaction-message-spec.js
--- a/lib/shared/messages/reaction-message-spec.js
+++ b/lib/shared/messages/reaction-message-spec.js
@@ -14,9 +14,9 @@
   assertMessageType,
   messageTypes,
 } from '../../types/message-types-enum.js';
-import {
-  type MessageInfo,
-  type ClientDBMessageInfo,
+import type {
+  MessageInfo,
+  ClientDBMessageInfo,
 } from '../../types/message-types.js';
 import {
   type ReactionMessageData,
@@ -218,5 +218,7 @@
     return action === 'add_reaction' ? pushTypes.NOTIF : pushTypes.RESCIND;
   },
 
+  canBeSidebarSource: false,
+
   validator: rawReactionMessageInfoValidator,
 });
diff --git a/lib/shared/messages/remove-members-message-spec.js b/lib/shared/messages/remove-members-message-spec.js
--- a/lib/shared/messages/remove-members-message-spec.js
+++ b/lib/shared/messages/remove-members-message-spec.js
@@ -166,5 +166,7 @@
     return rawMessageInfo.removedUserIDs;
   },
 
+  canBeSidebarSource: true,
+
   validator: rawRemoveMembersMessageInfoValidator,
 });
diff --git a/lib/shared/messages/restore-entry-message-spec.js b/lib/shared/messages/restore-entry-message-spec.js
--- a/lib/shared/messages/restore-entry-message-spec.js
+++ b/lib/shared/messages/restore-entry-message-spec.js
@@ -136,5 +136,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawRestoreEntryMessageInfoValidator,
 });
diff --git a/lib/shared/messages/sidebar-source-message-spec.js b/lib/shared/messages/sidebar-source-message-spec.js
--- a/lib/shared/messages/sidebar-source-message-spec.js
+++ b/lib/shared/messages/sidebar-source-message-spec.js
@@ -181,5 +181,7 @@
 
   startsThread: true,
 
+  canBeSidebarSource: false,
+
   validator: rawSidebarSourceMessageInfoValidator,
 });
diff --git a/lib/shared/messages/text-message-spec.js b/lib/shared/messages/text-message-spec.js
--- a/lib/shared/messages/text-message-spec.js
+++ b/lib/shared/messages/text-message-spec.js
@@ -314,5 +314,7 @@
     };
   },
 
+  canBeSidebarSource: true,
+
   validator: rawTextMessageInfoValidator,
 });
diff --git a/lib/shared/messages/toggle-pin-message-spec.js b/lib/shared/messages/toggle-pin-message-spec.js
--- a/lib/shared/messages/toggle-pin-message-spec.js
+++ b/lib/shared/messages/toggle-pin-message-spec.js
@@ -155,5 +155,7 @@
     return unwrapped;
   },
 
+  canBeSidebarSource: false,
+
   validator: rawTogglePinMessageInfoValidator,
 });
diff --git a/lib/shared/messages/unsupported-message-spec.js b/lib/shared/messages/unsupported-message-spec.js
--- a/lib/shared/messages/unsupported-message-spec.js
+++ b/lib/shared/messages/unsupported-message-spec.js
@@ -4,7 +4,7 @@
 
 import { pushTypes, type MessageSpec } from './message-spec.js';
 import { messageTypes } from '../../types/message-types-enum.js';
-import { type ClientDBMessageInfo } from '../../types/message-types.js';
+import type { ClientDBMessageInfo } from '../../types/message-types.js';
 import {
   type RawUnsupportedMessageInfo,
   type UnsupportedMessageInfo,
@@ -74,5 +74,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawUnsupportedMessageInfoValidator,
 });
diff --git a/lib/shared/messages/update-relationship-message-spec.js b/lib/shared/messages/update-relationship-message-spec.js
--- a/lib/shared/messages/update-relationship-message-spec.js
+++ b/lib/shared/messages/update-relationship-message-spec.js
@@ -177,5 +177,7 @@
 
   generatesNotifs: async () => pushTypes.NOTIF,
 
+  canBeSidebarSource: true,
+
   validator: rawUpdateRelationshipMessageInfoValidator,
 });
diff --git a/lib/types/message-types.test.js b/lib/types/message-types.test.js
--- a/lib/types/message-types.test.js
+++ b/lib/types/message-types.test.js
@@ -24,8 +24,9 @@
 import type { RawTogglePinMessageInfo } from './messages/toggle-pin.js';
 import type { RawUpdateRelationshipMessageInfo } from './messages/update-relationship.js';
 import { threadTypes } from './thread-types-enum.js';
+import { messageSpecs } from '../shared/messages/message-specs.js';
 
-describe('isInvalidSidebarSource', () => {
+describe('isInvalidSidebarSource & canBeSidebarSource', () => {
   it('should return false for RawTextMessageInfo', () => {
     const textMessageInfo: RawTextMessageInfo = {
       type: messageTypes.TEXT,
@@ -36,10 +37,14 @@
       text: 'This is a text message',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.TEXT];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(textMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawCreateThreadMessageInfo', () => {
@@ -57,11 +62,15 @@
       },
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CREATE_THREAD];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       createThreadMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawAddMembersMessageInfo', () => {
@@ -73,11 +82,15 @@
       addedUserIDs: ['4', '5'],
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.ADD_MEMBERS];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       addMembersMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawCreateSubthreadMessageInfo', () => {
@@ -89,11 +102,15 @@
       childThreadID: '10002',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CREATE_SUB_THREAD];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       createSubthreadMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawChangeSettingsMessageInfo', () => {
@@ -106,11 +123,15 @@
       value: '#FFFFFF',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CHANGE_SETTINGS];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       changeSettingsMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawRemoveMembersMessageInfo', () => {
@@ -122,11 +143,15 @@
       removedUserIDs: ['1', '2', '3'],
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.REMOVE_MEMBERS];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       removeMembersMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawChangeRoleMessageInfo', () => {
@@ -140,11 +165,15 @@
       roleName: 'Moderators',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CHANGE_ROLE];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       changeRoleMessageinfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawLeaveThreadMessageInfo', () => {
@@ -155,11 +184,15 @@
       time: 10000,
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.LEAVE_THREAD];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       leaveThreadMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawJoinThreadMessageInfo', () => {
@@ -170,11 +203,15 @@
       time: 10000,
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.JOIN_THREAD];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       joinThreadMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawCreateEntryMessageInfo', () => {
@@ -188,11 +225,15 @@
       text: 'This is a calendar entry',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CREATE_ENTRY];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       createEntryMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawEditEntryMessageInfo', () => {
@@ -206,10 +247,14 @@
       text: 'This is an edited calendar entry',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.EDIT_ENTRY];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(editEntryMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawDeleteEntryMessageInfo', () => {
@@ -223,11 +268,15 @@
       text: 'This is a deleted calendar entry',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.DELETE_ENTRY];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       deleteEntryMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawRestoreEntryMessageInfo', () => {
@@ -241,11 +290,15 @@
       text: 'This is a restored calendar entry',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.RESTORE_ENTRY];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       restoreEntryMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawUpdateRelationshipMessageInfo', () => {
@@ -258,11 +311,15 @@
       operation: 'request_sent',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.UPDATE_RELATIONSHIP];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       updateRelationshipMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawImagesMessageInfo', () => {
@@ -286,10 +343,14 @@
       ],
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.IMAGES];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(imageMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return false for RawMediaMessageInfo', () => {
@@ -313,10 +374,14 @@
       ],
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.MULTIMEDIA];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(mediaMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return true for RawSidebarSourceMessageInfo', () => {
@@ -336,11 +401,15 @@
       },
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.SIDEBAR_SOURCE];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       sidebarSourceMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(true);
+    expect(canBeSidebarSource).toBe(false);
   });
 
   it('should return false for RawCreateSidebarMessageInfo', () => {
@@ -358,11 +427,15 @@
       },
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.CREATE_SIDEBAR];
 
     const shouldBeInvalidSidebarSource = isInvalidSidebarSource(
       createSidebarMessageInfo,
     );
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(false);
+    expect(canBeSidebarSource).toBe(true);
   });
 
   it('should return true for RawReactionMessageInfo', () => {
@@ -377,10 +450,14 @@
       action: 'add_reaction',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.REACTION];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(reactionMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(true);
+    expect(canBeSidebarSource).toBe(false);
   });
 
   it('should return true for RawEditMessageInfo', () => {
@@ -393,10 +470,14 @@
       text: 'This is an edited message',
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.EDIT_MESSAGE];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(editMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(true);
+    expect(canBeSidebarSource).toBe(false);
   });
 
   it('should return true for RawTogglePinMessageInfo', () => {
@@ -410,9 +491,13 @@
       time: 10000,
       id: '1',
     };
+    const messageSpec = messageSpecs[messageTypes.TOGGLE_PIN];
 
     const shouldBeInvalidSidebarSource =
       isInvalidSidebarSource(togglePinMessageInfo);
+    const canBeSidebarSource = messageSpec.canBeSidebarSource;
+
     expect(shouldBeInvalidSidebarSource).toBe(true);
+    expect(canBeSidebarSource).toBe(false);
   });
 });