diff --git a/lib/shared/threads/protocols/dm-thread-protocol.js b/lib/shared/threads/protocols/dm-thread-protocol.js
--- a/lib/shared/threads/protocols/dm-thread-protocol.js
+++ b/lib/shared/threads/protocols/dm-thread-protocol.js
@@ -431,6 +431,8 @@
   },
 
   membershipChangesShownInThreadPreview: true,
+
+  allowsDeletingSidebarSource: false,
 });
 
 export { dmThreadProtocol };
diff --git a/lib/shared/threads/protocols/keyserver-thread-protocol.js b/lib/shared/threads/protocols/keyserver-thread-protocol.js
--- a/lib/shared/threads/protocols/keyserver-thread-protocol.js
+++ b/lib/shared/threads/protocols/keyserver-thread-protocol.js
@@ -214,6 +214,8 @@
   },
 
   membershipChangesShownInThreadPreview: false,
+
+  allowsDeletingSidebarSource: true,
 });
 
 function mediaIDIsKeyserverID(mediaID: string): boolean {
diff --git a/lib/shared/threads/thread-spec.js b/lib/shared/threads/thread-spec.js
--- a/lib/shared/threads/thread-spec.js
+++ b/lib/shared/threads/thread-spec.js
@@ -185,6 +185,7 @@
     utils: SetThreadUnreadStatusUtils,
   ) => Promise<SetThreadUnreadStatusPayload>,
   +membershipChangesShownInThreadPreview: boolean,
+  +allowsDeletingSidebarSource: boolean,
 };
 
 export type ThreadSpec = {
diff --git a/lib/utils/delete-message-utils.js b/lib/utils/delete-message-utils.js
--- a/lib/utils/delete-message-utils.js
+++ b/lib/utils/delete-message-utils.js
@@ -14,15 +14,13 @@
 } from '../shared/dm-ops/dm-op-types.js';
 import { useProcessAndSendDMOperation } from '../shared/dm-ops/process-dm-ops.js';
 import { useThreadHasPermission } from '../shared/thread-utils.js';
+import { threadSpecs } from '../shared/threads/thread-specs.js';
 import type { DMSendDeleteMessageOperation } from '../types/dm-ops.js';
 import type { MessageInfo } from '../types/message-types.js';
 import { isComposableMessageType } from '../types/message-types.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import {
-  thickThreadTypes,
-  threadTypeIsThick,
-} from '../types/thread-types-enum.js';
+import { thickThreadTypes } from '../types/thread-types-enum.js';
 
 const deletedMessageText = 'Deleted message';
 
@@ -108,12 +106,8 @@
     return false;
   }
 
-  if (canDeleteAllMessages) {
-    return true;
-  }
-
   if (
-    threadTypeIsThick(threadInfo.type) &&
+    !threadSpecs[threadInfo.type].protocol.allowsDeletingSidebarSource &&
     (targetMessageInfo.time < threadInfo.creationTime ||
       threadCreatedFromMessage)
   ) {
@@ -123,6 +117,10 @@
     return false;
   }
 
+  if (canDeleteAllMessages) {
+    return true;
+  }
+
   return (
     currentUserInfo.id === targetMessageInfo.creator.id && canDeleteOwnMessages
   );