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
@@ -25,7 +25,6 @@
 } from '../../types/messages/add-members.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import { threadIDIsThick } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -34,6 +33,7 @@
 } from '../../utils/entity-text.js';
 import { values } from '../../utils/objects.js';
 import { notifRobotextForMessageInfo } from '../notif-utils.js';
+import { getProtocolByThreadID } from '../threads/protocols/thread-protocols.js';
 import { threadSpecs } from '../threads/thread-specs.js';
 
 function getAddMembersRobotext(messageInfo: AddMembersMessageInfo): EntityText {
@@ -246,7 +246,6 @@
       : null,
 
   getMessageNotifyType: async (rawMessageInfo: RawAddMembersMessageInfo) =>
-    threadIDIsThick(rawMessageInfo.threadID)
-      ? messageNotifyTypes.SET_UNREAD
-      : messageNotifyTypes.NONE,
+    getProtocolByThreadID(rawMessageInfo.threadID)
+      ?.membershipMessageNotifAction ?? messageNotifyTypes.NONE,
 });
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
@@ -24,7 +24,6 @@
 } from '../../types/messages/join-thread.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import { threadIDIsThick } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -32,6 +31,7 @@
   pluralizeEntityText,
 } from '../../utils/entity-text.js';
 import { values } from '../../utils/objects.js';
+import { getProtocolByThreadID } from '../threads/protocols/thread-protocols.js';
 import { threadSpecs } from '../threads/thread-specs.js';
 
 function getJoinThreadRobotext(
@@ -192,7 +192,6 @@
       : null,
 
   getMessageNotifyType: async (rawMessageInfo: RawJoinThreadMessageInfo) =>
-    threadIDIsThick(rawMessageInfo.threadID)
-      ? messageNotifyTypes.SET_UNREAD
-      : messageNotifyTypes.NONE,
+    getProtocolByThreadID(rawMessageInfo.threadID)
+      ?.membershipMessageNotifAction ?? messageNotifyTypes.NONE,
 });
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
@@ -24,7 +24,6 @@
 } from '../../types/messages/leave-thread.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import { threadIDIsThick } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -32,6 +31,7 @@
   pluralizeEntityText,
 } from '../../utils/entity-text.js';
 import { values } from '../../utils/objects.js';
+import { getProtocolByThreadID } from '../threads/protocols/thread-protocols.js';
 import { threadSpecs } from '../threads/thread-specs.js';
 
 function getLeaveThreadRobotext(
@@ -192,7 +192,6 @@
       : null,
 
   getMessageNotifyType: async (rawMessageInfo: RawLeaveThreadMessageInfo) =>
-    threadIDIsThick(rawMessageInfo.threadID)
-      ? messageNotifyTypes.SET_UNREAD
-      : messageNotifyTypes.NONE,
+    getProtocolByThreadID(rawMessageInfo.threadID)
+      ?.membershipMessageNotifAction ?? messageNotifyTypes.NONE,
 });
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
@@ -25,7 +25,6 @@
 } from '../../types/messages/remove-members.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import { threadIDIsThick } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -34,6 +33,7 @@
 } from '../../utils/entity-text.js';
 import { values } from '../../utils/objects.js';
 import { notifRobotextForMessageInfo } from '../notif-utils.js';
+import { getProtocolByThreadID } from '../threads/protocols/thread-protocols.js';
 import { threadSpecs } from '../threads/thread-specs.js';
 
 function getRemoveMembersRobotext(
@@ -251,11 +251,8 @@
         ? rawMessageInfo.time
         : null,
 
-    getMessageNotifyType: async (
-      rawMessageInfo: RawRemoveMembersMessageInfo,
-    ) =>
-      threadIDIsThick(rawMessageInfo.threadID)
-        ? messageNotifyTypes.SET_UNREAD
-        : messageNotifyTypes.NONE,
+    getMessageNotifyType: async (rawMessageInfo: RawRemoveMembersMessageInfo) =>
+      getProtocolByThreadID(rawMessageInfo.threadID)
+        ?.membershipMessageNotifAction ?? messageNotifyTypes.NONE,
   },
 );
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
@@ -51,6 +51,7 @@
 import {
   assertWithValidator,
   pendingThickSidebarURLPrefix,
+  thickIDRegex,
 } from '../../../utils/validation-utils.js';
 import { generatePendingThreadColor } from '../../color-utils.js';
 import {
@@ -58,6 +59,7 @@
   type OutboundDMOperationSpecification,
 } from '../../dm-ops/dm-op-types.js';
 import { getIDFromLocalID } from '../../id-utils.js';
+import { messageNotifyTypes } from '../../messages/message-spec.js';
 import {
   createThreadTimestamps,
   getContainingThreadID,
@@ -881,6 +883,8 @@
       }: ThreadJoinPayload);
     },
 
+    threadIDMatchesProtocol: (threadID: string) => thickIDRegex.test(threadID),
+
     allowsDeletingSidebarSource: false,
 
     presentationDetails: {
@@ -909,6 +913,8 @@
     arePendingThreadsDescendantsOfGenesis: false,
 
     threadActivityUpdatedByDMActivityHandler: true,
+
+    membershipMessageNotifAction: messageNotifyTypes.SET_UNREAD,
   });
 
 function pendingThreadType(numberOfOtherMembers: number) {
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
@@ -68,9 +68,14 @@
   getMessageForException,
   SendMessageError,
 } from '../../../utils/errors.js';
-import { pendingSidebarURLPrefix } from '../../../utils/validation-utils.js';
+import {
+  isSchemaRegExp,
+  pendingSidebarURLPrefix,
+  thickIDRegex,
+} from '../../../utils/validation-utils.js';
 import { generatePendingThreadColor } from '../../color-utils.js';
 import { getNextLocalID } from '../../id-utils.js';
+import { messageNotifyTypes } from '../../messages/message-spec.js';
 import {
   getCommunity,
   getContainingThreadID,
@@ -634,6 +639,10 @@
       return await utils.keyserverJoinThread(request);
     },
 
+    threadIDMatchesProtocol: (threadID: string) => {
+      return isSchemaRegExp.test(threadID) && !thickIDRegex.test(threadID);
+    },
+
     allowsDeletingSidebarSource: true,
 
     presentationDetails: {
@@ -662,6 +671,8 @@
     arePendingThreadsDescendantsOfGenesis: true,
 
     threadActivityUpdatedByDMActivityHandler: false,
+
+    membershipMessageNotifAction: messageNotifyTypes.NONE,
   });
 
 function pendingThreadType(numberOfOtherMembers: number) {
diff --git a/lib/shared/threads/protocols/thread-protocols.js b/lib/shared/threads/protocols/thread-protocols.js
--- a/lib/shared/threads/protocols/thread-protocols.js
+++ b/lib/shared/threads/protocols/thread-protocols.js
@@ -9,4 +9,8 @@
   keyserverThreadProtocol,
 ];
 
-export { protocols };
+function getProtocolByThreadID(threadID: string): ?ThreadProtocol<any> {
+  return protocols().find(p => p.threadIDMatchesProtocol(threadID));
+}
+
+export { protocols, getProtocolByThreadID };
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
@@ -85,6 +85,7 @@
   OutboundDMOperationSpecification,
 } from '../dm-ops/dm-op-types.js';
 import type { FetchThickMessagesType } from '../message-utils.js';
+import type { MessageNotifyType } from '../messages/message-spec.js';
 import type { CreatePendingThreadArgs } from '../thread-utils.js';
 
 export type ThreadTrait =
@@ -371,6 +372,7 @@
     input: ProtocolJoinThreadInput,
     utils: JoinThreadUtils,
   ) => Promise<ThreadJoinPayload>,
+  +threadIDMatchesProtocol: string => boolean,
   +allowsDeletingSidebarSource: boolean,
   +presentationDetails: {
     +membershipChangesShownInThreadPreview: boolean,
@@ -393,6 +395,7 @@
   // This flag is temporary. It should be deleted as a part of
   // https://linear.app/comm/issue/ENG-10729/consider-merging-activity-handlers
   +threadActivityUpdatedByDMActivityHandler: boolean,
+  +membershipMessageNotifAction: MessageNotifyType,
 };
 
 export type ThreadSpec<
diff --git a/lib/utils/validation-utils.js b/lib/utils/validation-utils.js
--- a/lib/utils/validation-utils.js
+++ b/lib/utils/validation-utils.js
@@ -111,6 +111,7 @@
 const uuidRegex =
   '[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}';
 const idSchemaRegex = `(?:(?:[0-9]+|${uuidRegex})\\|)?(?:[0-9]+|${uuidRegex})`;
+const isSchemaRegExp: RegExp = new RegExp(`^${idSchemaRegex}$`);
 
 const pendingSidebarURLPrefix = 'sidebar';
 const pendingThickSidebarURLPrefix = 'dm_sidebar';
@@ -156,4 +157,5 @@
   validChatNameRegex,
   validChatNameRegexString,
   chatNameMaxLength,
+  isSchemaRegExp,
 };