diff --git a/src/db/interfaces.ts b/src/db/interfaces.ts
index 46c34f4e..b6e1d4ac 100644
--- a/src/db/interfaces.ts
+++ b/src/db/interfaces.ts
@@ -147,6 +147,16 @@ export interface MessageRecord {
   text_fallback?: boolean;
   /** What a webhook posted under. Enrichment turns it into sender_nickname. */
   sender_display_name?: string | null;
+  /** Set on the notice the server writes for apps from before MLS, sent as "system".
+      Apps that read MLS hide these rows (GRYT-1508). */
+  mls_placeholder?: MlsPlaceholder;
+}
+
+export interface MlsPlaceholder {
+  /** The entry in the conversation's MLS group log this row stands in for. */
+  seq: number;
+  /** Who really sent it, so a block hides the notice too. */
+  sender_server_id: string;
 }
 
 export interface StoredWebhookCard {
diff --git a/src/db/sqlite/connection.ts b/src/db/sqlite/connection.ts
index 559a736e..c6db13ce 100644
--- a/src/db/sqlite/connection.ts
+++ b/src/db/sqlite/connection.ts
@@ -929,6 +929,12 @@ function runMigrations(d: DatabaseSync): void {
   if (!hasColumn(d, "messages", "sender_avatar_file_id")) {
     d.exec("ALTER TABLE messages ADD COLUMN sender_avatar_file_id TEXT");
   }
+  // A placeholder the server writes for apps from before MLS, and whose MLS message
+  // it stands in for (GRYT-1508). NULL on every other row.
+  if (!hasColumn(d, "messages", "mls_seq")) {
+    d.exec("ALTER TABLE messages ADD COLUMN mls_seq INTEGER");
+    d.exec("ALTER TABLE messages ADD COLUMN mls_sender_server_id TEXT");
+  }
   // One stored file per picture a webhook sends, however often it sends it.
   d.exec(`CREATE TABLE IF NOT EXISTS webhook_media (
     webhook_id TEXT NOT NULL,
diff --git a/src/db/sqlite/contactPrefs.ts b/src/db/sqlite/contactPrefs.ts
index af4d428a..002f80c8 100644
--- a/src/db/sqlite/contactPrefs.ts
+++ b/src/db/sqlite/contactPrefs.ts
@@ -47,11 +47,13 @@ export async function setContactPrefs(grytUserId: string, prefs: ContactPrefs):
   ).run(grytUserId, prefs.messages, prefs.calls, toIso(new Date()));
 }
 
-/** Whether `author` has sent anything in their one-to-one with `other`. The
-    sender column is stored for sealed messages too, so this works on those. */
+/** Whether `author` has sent anything in their one-to-one with `other`. Sealed messages
+    keep their sender, and an MLS one counts through its placeholder. */
 export async function hasWrittenTo(authorServerUserId: string, otherServerUserId: string): Promise<boolean> {
   const row = getSqliteDb()
-    .prepare(`SELECT 1 FROM messages WHERE conversation_id = ? AND sender_server_id = ? LIMIT 1`)
-    .get(directConversationId(authorServerUserId, otherServerUserId), authorServerUserId);
+    .prepare(
+      `SELECT 1 FROM messages WHERE conversation_id = ? AND (sender_server_id = ? OR mls_sender_server_id = ?) LIMIT 1`,
+    )
+    .get(directConversationId(authorServerUserId, otherServerUserId), authorServerUserId, authorServerUserId);
   return !!row;
 }
diff --git a/src/db/sqlite/mergeGuest.ts b/src/db/sqlite/mergeGuest.ts
index 7db2fc49..f9f0cda0 100644
--- a/src/db/sqlite/mergeGuest.ts
+++ b/src/db/sqlite/mergeGuest.ts
@@ -17,6 +17,7 @@ export interface GuestMerge {
     fails when a new column that can hold a server user id is not accounted for. */
 export const AUTHOR_COLUMNS: ReadonlyArray<readonly [table: string, column: string]> = [
   ["messages", "sender_server_id"],
+  ["messages", "mls_sender_server_id"],
   ["threads", "created_by"],
   ["conversations", "created_by_server_user_id"],
   ["files", "uploaded_by_server_user_id"],
diff --git a/src/db/sqlite/messages.ts b/src/db/sqlite/messages.ts
index a78f32a3..e01dba35 100644
--- a/src/db/sqlite/messages.ts
+++ b/src/db/sqlite/messages.ts
@@ -21,6 +21,9 @@ function rowToMessage(r: Record<string, unknown>): MessageRecord {
     ...(r.text_fallback ? { text_fallback: true } : {}),
     ...(r.sender_display_name ? { sender_display_name: r.sender_display_name as string } : {}),
     ...(r.sender_avatar_file_id ? { sender_avatar_file_id: r.sender_avatar_file_id as string } : {}),
+    ...(r.mls_seq != null
+      ? { mls_placeholder: { seq: Number(r.mls_seq), sender_server_id: r.mls_sender_server_id as string } }
+      : {}),
   };
 }
 
@@ -32,7 +35,7 @@ export async function insertMessage(record: Omit<MessageRecord, "message_id" | "
   const message_id = record.message_id ?? randomUUID();
 
   db.prepare(
-    `INSERT INTO messages (conversation_id, message_id, sender_server_id, text, sealed, attachments, reactions, reply_to_message_id, thread_id, cards, text_fallback, sender_display_name, sender_avatar_file_id, created_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+    `INSERT INTO messages (conversation_id, message_id, sender_server_id, text, sealed, attachments, reactions, reply_to_message_id, thread_id, cards, text_fallback, sender_display_name, sender_avatar_file_id, mls_seq, mls_sender_server_id, created_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
   ).run(
     record.conversation_id,
     message_id,
@@ -47,6 +50,8 @@ export async function insertMessage(record: Omit<MessageRecord, "message_id" | "
     record.text_fallback ? 1 : 0,
     record.sender_display_name ?? null,
     record.sender_avatar_file_id ?? null,
+    record.mls_placeholder?.seq ?? null,
+    record.mls_placeholder?.sender_server_id ?? null,
     toIso(created_at),
   );
 
diff --git a/src/socket/handlers/chat.ts b/src/socket/handlers/chat.ts
index 2427c607..7a69a81c 100644
--- a/src/socket/handlers/chat.ts
+++ b/src/socket/handlers/chat.ts
@@ -886,7 +886,7 @@ export function registerChatHandlers(ctx: HandlerContext): EventHandlerMap {
         const hidden = await blockedServerIdsFor(clientsInfo[clientId]?.serverUserId ?? "");
         const visible = hidden.size === 0
           ? items
-          : items.filter((m) => !hidden.has(m.sender_server_id));
+          : items.filter((m) => !hidden.has(m.sender_server_id) && !hidden.has(m.mls_placeholder?.sender_server_id ?? ""));
 
         let enrichedItems = await enrichMessages(visible);
         enrichedItems = await enrichAttachments(enrichedItems);
diff --git a/src/socket/handlers/mls.test.ts b/src/socket/handlers/mls.test.ts
index 340c2fdf..9f9b5a48 100644
--- a/src/socket/handlers/mls.test.ts
+++ b/src/socket/handlers/mls.test.ts
@@ -14,6 +14,8 @@ import { setContactPrefs } from "../../db/sqlite/contactPrefs";
 import { createGroupConversation, openDirectConversation } from "../../db/sqlite/conversations";
 import { getMlsGroupForConversation } from "../../db/sqlite/mls";
 import { createServerConfigIfNotExists, setServerRole, updateServerConfig } from "../../db/sqlite/servers";
+import { hasWrittenTo } from "../../db/sqlite/contactPrefs";
+import { listMessages } from "../../db/sqlite/messages";
 import { setUserModerationState, upsertUser } from "../../db/sqlite/users";
 import { mlsRetentionDays, runMlsRetention } from "../../jobs/mlsRetention";
 import { parseGroupMessage, parseKeyPackage, parseWelcome } from "../../services/mlsWire";
@@ -21,6 +23,7 @@ import type { Clients } from "../../types";
 import { generateAccessToken } from "../../utils/jwt";
 import { resetChannelIdCache } from "../utils/conversationAccess";
 import { refreshClientPermissions } from "../utils/standing";
+import { registerChatHandlers } from "./chat";
 import { registerMlsHandlers } from "./mls";
 import type { EventHandlerMap, HandlerContext } from "./types";
 
@@ -101,7 +104,7 @@ async function connect(nickname: string): Promise<Participant> {
     getClientIp: () => `10.9.0.${seq}`,
     clientAddressIsOwn: () => true,
   } as unknown as HandlerContext;
-  const handlers = registerMlsHandlers(ctx);
+  const handlers = { ...registerChatHandlers(ctx), ...registerMlsHandlers(ctx) };
   const accessToken = generateAccessToken({ grytUserId, serverUserId: user.server_user_id, nickname, serverHost: HOST, tokenVersion: 0 });
 
   return {
@@ -422,6 +425,18 @@ describe("a DM over MLS", () => {
     assert.equal(bob.received("dm:opened").length, 1, "the first message puts the conversation in Bob's list");
   });
 
+  it("leaves apps from before MLS a line saying there's a message, marked so newer ones hide it", async () => {
+    const [line] = bob.received("chat:new");
+    assert.equal(line.sender_server_id, "system", "a system line, since a plain one would carry the old app's Not encrypted mark");
+    assert.equal(line.text, `[@Alice](mention:${alice.serverUserId}) sent an end-to-end encrypted message. Update Gryt to read it.`);
+    assert.deepEqual(line.mls_placeholder, { seq: 2, sender_server_id: alice.serverUserId });
+    assert.deepEqual(alice.received("chat:new"), [], "not to the sender, whose own old apps find it in history");
+
+    const stored = (await listMessages(dm)).filter((m) => m.mls_placeholder);
+    assert.deepEqual(stored.map((m) => m.mls_placeholder?.seq), [2]);
+    assert.equal(await hasWrittenTo(alice.serverUserId, bob.serverUserId), true, "so contact settings see the MLS message");
+  });
+
   it("tells the other side about a new device, and lists devices by conversation", async () => {
     alice.clear();
     const b2 = await makeDevice("bob-laptop", 1);
@@ -520,6 +535,10 @@ describe("a DM over MLS", () => {
     a1.state = c.newState;
 
     assert.deepEqual(bob.received("mls:message").map((m) => m.kind), ["commit"]);
+    assert.deepEqual(bob.received("chat:new"), [], "nor the line for older apps");
+    await bob.handlers["chat:fetch"]({ conversationId: dm, limit: 50 });
+    const history = bob.received("chat:history")[0] as { items: { mls_placeholder?: { sender_server_id: string } }[] };
+    assert.ok(!history.items.some((m) => m.mls_placeholder), "and history leaves it out too");
     const fetched = await bob.call("mls:log:fetch", { conversationId: dm, after: head });
     assert.deepEqual((fetched.entries as { kind: string }[]).map((e) => e.kind), ["commit"]);
     assert.equal(fetched.nextCursor, head + 2, "the cursor still moves past what was held back");
@@ -538,6 +557,19 @@ describe("a DM over MLS", () => {
     const r = await alice.call("mls:group:create", { conversationId: group.conversation_id, groupId: "cd" });
     assert.equal(r.error, "not_supported");
   });
+
+  it("leaves no line for what isn't a message", async () => {
+    bob.clear();
+    const before = (await listMessages(dm)).length;
+    const quiet = await alice.call("mls:send", { conversationId: dm, deviceId: a1.id, message: await applicationMessage(a1, "a reaction"), placeholder: false });
+    assert.equal(quiet.ok, true);
+    assert.equal(bob.received("mls:message").length, 1);
+    assert.deepEqual(bob.received("chat:new"), []);
+    assert.equal((await listMessages(dm)).length, before);
+
+    const odd = await alice.call("mls:send", { conversationId: dm, deviceId: a1.id, message: await applicationMessage(a1, "x"), placeholder: "no" });
+    assert.equal(odd.error, "invalid_payload");
+  });
 });
 
 describe("retention", () => {
diff --git a/src/socket/handlers/mls.ts b/src/socket/handlers/mls.ts
index f8de0cc5..cdf3359b 100644
--- a/src/socket/handlers/mls.ts
+++ b/src/socket/handlers/mls.ts
@@ -15,6 +15,7 @@ import {
   getMlsGroupForConversation,
   getServerConfig,
   getUserByServerId,
+  insertMessage,
   isMlsDevice,
   listConversationsForUser,
   listMlsDevices,
@@ -37,6 +38,8 @@ import { textMuteError, textMuteFor } from "../../moderation/textMute";
 import { mayInChannel } from "../../services/channelPermissions";
 import { asBytes, parseGroupMessage, parseKeyPackage, parseWelcome } from "../../services/mlsWire";
 import { SEALED_MAX_LENGTH } from "../../utils/messageLimits";
+import { appendCachedMessage } from "../utils/messageCache";
+import { formatMlsPlaceholder, SYSTEM_SENDER_ID } from "../utils/systemMessages";
 import { checkRateLimit, type RateLimitRule } from "../../utils/rateLimiter";
 import { requireAuth, type AuthResult } from "../middleware/auth";
 import { CONTACT_REFUSALS, mayMessage, peerOf } from "../utils/contactGate";
@@ -239,6 +242,26 @@ export function registerMlsHandlers(ctx: HandlerContext): EventHandlerMap {
     emitTo(recipients, "mls:message", entryView(conversationId, entry));
   }
 
+  /* The line apps from before MLS show instead (GRYT-1508). Not to the sender's own
+     sockets: their old apps find it in history, and aren't notified about themselves. */
+  async function writePlaceholder(self: string, memberIds: string[], conversationId: string, seq: number, createdAt: string): Promise<void> {
+    const sender = await getUserByServerId(self);
+    if (!sender) return;
+    const msg = await insertMessage({
+      conversation_id: conversationId,
+      sender_server_id: SYSTEM_SENDER_ID,
+      text: formatMlsPlaceholder(sender.nickname, sender.server_user_id),
+      attachments: null,
+      reactions: null,
+      mls_placeholder: { seq, sender_server_id: sender.server_user_id },
+      created_at: new Date(createdAt),
+    });
+    appendCachedMessage(conversationId, msg);
+    const blockers = await blockersOfSender(sender.server_user_id);
+    const audience = memberIds.filter((id) => id !== sender.server_user_id && !blockers.has(id));
+    emitTo(socketsOf(audience), "chat:new", { ...msg, sender_nickname: "System", sender_avatar_file_id: undefined });
+  }
+
   /* Whoever shares a DM with them adds the new device the next time they send. */
   async function announceDevices(serverUserId: string): Promise<void> {
     const people = new Set([serverUserId]);
@@ -529,13 +552,17 @@ export function registerMlsHandlers(ctx: HandlerContext): EventHandlerMap {
 
     /** An application message (PrivateMessage) or a proposal (PublicMessage). */
     "mls:send": async (
-      payload: { accessToken: string; conversationId: string; deviceId: string; message: unknown },
+      payload: { accessToken: string; conversationId: string; deviceId: string; message: unknown; placeholder?: unknown },
       ack: Ack,
     ) => {
       ack = typeof ack === "function" ? ack : () => {};
       try {
         const auth = await begin("mls:send", RL_SEND, payload, ack);
         if (!auth || !ownDevice(auth, payload.deviceId, ack)) return;
+        if (payload.placeholder !== undefined && typeof payload.placeholder !== "boolean") {
+          ack(fail("invalid_payload", "placeholder has to be true or false."));
+          return;
+        }
         const self = auth.tokenPayload.serverUserId;
         const memberIds = await dmOf(payload.conversationId, self, ack);
         if (!memberIds) return;
@@ -614,6 +641,12 @@ export function registerMlsHandlers(ctx: HandlerContext): EventHandlerMap {
           groupId: group.groupId, seq: result.seq, kind: parsed.kind, epoch: parsed.epoch,
           senderServerUserId: self, senderDeviceId: payload.deviceId, data: bytes, createdAt: result.createdAt,
         }, payload.conversationId);
+        // A reaction, edit or delete says false, or old apps show a line for each one.
+        if (application && payload.placeholder !== false) {
+          await writePlaceholder(self, memberIds, payload.conversationId, result.seq, result.createdAt).catch((err) =>
+            consola.warn("mls placeholder failed", payload.conversationId, err),
+          );
+        }
         ack({ ok: true, seq: result.seq });
       } catch (err) {
         consola.error("mls:send failed", err);
diff --git a/src/socket/utils/systemMessages.ts b/src/socket/utils/systemMessages.ts
index 70664b4d..53061917 100644
--- a/src/socket/utils/systemMessages.ts
+++ b/src/socket/utils/systemMessages.ts
@@ -5,7 +5,7 @@ import { getServerConfig, insertMessage, listServerChannels } from "../../db";
 import type { Clients } from "../../types";
 import { recipientClientIds } from "./recipients";
 
-const SYSTEM_SENDER_ID = "system";
+export const SYSTEM_SENDER_ID = "system";
 
 let cachedChannelId: string | null = null;
 let channelCacheFetchedAt = 0;
@@ -77,6 +77,12 @@ export function formatJoinMessage(nickname: string, serverUserId: string): strin
   return `[@${nickname}](mention:${serverUserId}) joined the server`;
 }
 
+/** What an app from before MLS shows for an MLS message (GRYT-1508). Plain text there
+    would carry that app's "Not encrypted" mark, so it goes out as a system line. */
+export function formatMlsPlaceholder(nickname: string, serverUserId: string): string {
+  return `[@${nickname}](mention:${serverUserId}) sent an end-to-end encrypted message. Update Gryt to read it.`;
+}
+
 export function formatLeaveMessage(nickname: string, serverUserId: string): string {
   return `[@${nickname}](mention:${serverUserId}) left the server`;
 }