diff --git a/docs/systems/dm-system.md b/docs/systems/dm-system.md
index 710d015b..ac9fda2c 100644
--- a/docs/systems/dm-system.md
+++ b/docs/systems/dm-system.md
@@ -283,7 +283,7 @@ If a `member_add` federation event arrives for a soft-deleted channel (non-null
 
 **Request:** `{ content?: string, attachments?: string[], replyToId?: string }`
 
-**Cross-instance access:** Federated users (those with `homeInstance` set) can send messages on any DM channel where they are a member, regardless of which instance serves the request. The `requireLocalUser` gate that previously blocked federated users from DM write endpoints has been removed. DM calls work across federated instances. The caller's instance hosts the LiveKit room; remote clients connect directly. Call signaling is relayed to all active federation peers via synchronous HTTP POST (not the outbox worker). Relay failures at any call state transition emit `dm_call_undeliverable { phase, terminal, failures }` to the originator — see `docs/systems/voice.md` for the full call state machine and failure surface.
+**Cross-instance access:** Federated users (those with `homeInstance` set) can send messages on any DM channel where they are a member, regardless of which instance serves the request. The `requireLocalUser` gate that previously blocked federated users from DM write endpoints has been removed. DM calls work across federated instances. The caller's instance hosts the LiveKit room; remote clients connect directly. Call signaling is relayed to all active federation peers via synchronous HTTP POST (not the outbox worker). Relay failures at any call state transition emit `dm_call_undeliverable { phase, terminal, failures }` to the originator — see `docs/systems/voice.md` for the full call state machine and failure surface. Federated call-start to a remote instance with no reachable recipient surfaces as `dm_call_undeliverable` with reason `no_recipient` — see `voice.md` for the full failure-surface table.
 
 **Validation:**
 - Caller must be a member (`isDmMember`)
diff --git a/docs/systems/federation.md b/docs/systems/federation.md
index 8e69dc62..9f817d57 100644
--- a/docs/systems/federation.md
+++ b/docs/systems/federation.md
@@ -529,10 +529,42 @@ interface FederationRelayResponse {
     messageId: string;
     reason: string;                // e.g., 'duplicate', 'unknown_message', 'missing_participants'
   }>;
+  undeliverable?: Array<{          // optional — omitted when empty; call-signaling only
+    messageId: string;
+    reason: string;                // e.g., 'no_recipient'
+  }>;
   maxUploadSize: number;           // This instance's max upload size in bytes
 }
 ```
 
+#### `undeliverable` bucket (call-signaling only)
+
+In addition to `accepted` and `rejected`, the relay response may include an
+optional `undeliverable: Array<{messageId, reason}>`. Three-way classification,
+non-overlapping: each messageId appears in exactly one of the three arrays.
+
+| Bucket | Meaning | Retry? |
+|---|---|---|
+| `accepted` | Processed cleanly, ≥1 recipient reached. | No |
+| `rejected` | Refused at data/protocol layer (schema, attribution, channel-not-found, etc.). | Terminal. |
+| `undeliverable` | Processed cleanly, zero recipients reachable. | No — call-signaling specific. |
+
+Currently used only for `dm_call_start`:
+- **Path A** (local DM exists): if no local non-caller member has an active WS
+  connection, the event is pushed to `undeliverable` with reason `no_recipient`
+  instead of being silently accepted. No `FederatedCallEntry` is created.
+- **Path B** (no local DM): the zero-participant-match early return pushes to
+  `undeliverable` rather than `accepted`.
+
+Other event types (messages, reactions, friend events, profile updates, etc.)
+keep existing semantics — a message to an offline user is still `accepted`, since
+messages persist and re-deliver on reconnect.
+
+The field is optional on the wire. Old peers omit it; new peers include it only
+when non-empty. Caller-side `sendCallRelay` parses the field (defaulting to an
+empty array when missing), so upgrade skew is a no-op until both sides are on
+new code.
+
 ### Inbound Relay Dispatch (`POST /api/federation/relay`)
 
 Body limit: 10 MB. Max 50 events per batch. Rate-limited to 90 requests/min per peer (sliding window, keyed by `peer.origin`). Returns 429 when exceeded. Raised from 30 after FED-009 reduced the outbox worker interval from 10s to 1s — a busy sender can now hit 60 req/min during sustained traffic.
diff --git a/docs/systems/voice.md b/docs/systems/voice.md
index 7d396a7c..8ee143b5 100644
--- a/docs/systems/voice.md
+++ b/docs/systems/voice.md
@@ -71,6 +71,7 @@ All `dm_call_*` signaling events (`start`, `accept`, `reject`, `end`) are relaye
 | `reject` | false | Rejector's relay to host failed OR host's fan-out after a local reject failed; state already cleared. | No state change; info toast. |
 | `end` | false | Ender's relay to host failed OR host's fan-out after a local end failed; state already cleared. | No state change; info toast. |
 | `host_unreachable` | true | A FederatedCallEntry's `federatedCallHost` peer transitions out of `active`, OR the 30s sentinel detects a non-active host for an existing entry. | Clear `activeDmCall` + `incomingCall`, disconnect LK, warning toast (*"Call ended — {label} became unreachable."*). |
+| `no_recipient` | true | Remote returned 200 but had no reachable recipient (Path A: all members offline; Path B: zero participant matches). Caller fast-fails within the relay round-trip; ring room destroyed. | Clear `outgoingCall`, disconnect LK, warning toast (*"{peerLabel} couldn't ring anyone."*). Folds into multi-failure info copy when not the sole failure. |
 
 **Accept-rollback semantics.** `handleDmCallAccept` Path 2 transitions the `FederatedCallEntry` to active and broadcasts `dm_call_accepted` optimistically so the acceptor's UI flips immediately. If the B→host relay fails, the server clears the entry, fans `dm_call_undeliverable { phase: 'accept', terminal: true }` out to all ringed users on B (via `sendToFederatedCallUsers`), and the client tears its call state back down.
 
diff --git a/docs/systems/websocket.md b/docs/systems/websocket.md
index 0d40582f..51dee891 100644
--- a/docs/systems/websocket.md
+++ b/docs/systems/websocket.md
@@ -170,7 +170,7 @@ reason: `'displaced'` (new tab) | `'session_closed'`
 | `dm_call_accepted` | dmChannelId?, federatedCallId? | DM members |
 | `dm_call_rejected` | dmChannelId?, federatedCallId? | DM members |
 | `dm_call_ended` | dmChannelId?, federatedCallId? | DM members |
-| `dm_call_undeliverable` | Sent to the originator when a call relay (start / accept / reject / end) to one or more peers fails. Includes `phase: 'start' \| 'accept' \| 'reject' \| 'end'` identifying the action; `failures[]` enumerates failed peers with a `reason` (`peer_rejected` / `peer_awaiting_approval` / `peer_transient_failure` / `livekit_unavailable`). `terminal: true` means local call state should be (or has been) torn down; `terminal: false` is informational. See `docs/systems/voice.md` for the full phase × terminal matrix. | originator (caller / acceptor / rejector / ender) |
+| `dm_call_undeliverable` | Sent to the originator when a call relay (start / accept / reject / end) to one or more peers fails. Includes `phase: 'start' \| 'accept' \| 'reject' \| 'end' \| 'host_unreachable'` identifying the action; `failures[]` enumerates failed peers with a `reason` (`peer_rejected` / `peer_awaiting_approval` / `peer_transient_failure` / `livekit_unavailable` / `no_recipient`). `terminal: true` means local call state should be (or has been) torn down; `terminal: false` is informational. See `docs/systems/voice.md` for the full phase × terminal matrix. | originator (caller / acceptor / rejector / ender) |
 
 ### Social
 | type | fields | scope |
diff --git a/packages/server/src/routes/federation.callStart.test.ts b/packages/server/src/routes/federation.callStart.test.ts
new file mode 100644
index 00000000..9ba88114
--- /dev/null
+++ b/packages/server/src/routes/federation.callStart.test.ts
@@ -0,0 +1,248 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { drizzle } from 'drizzle-orm/better-sqlite3';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import type WebSocket from 'ws';
+import * as schema from '../db/schema.js';
+import { setWorkerId } from '../utils/snowflake.js';
+
+setWorkerId(1);
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+type TestDb = ReturnType<typeof drizzle<typeof schema>>;
+let testDb: TestDb;
+
+vi.mock('../db/index.js', () => ({
+  getDb: () => testDb,
+  schema,
+}));
+
+vi.mock('../utils/federationAuth.js', async () => {
+  const actual = await vi.importActual<typeof import('../utils/federationAuth.js')>(
+    '../utils/federationAuth.js',
+  );
+  return {
+    ...actual,
+    getOurOrigin: () => 'https://local.example',
+  };
+});
+
+function applyMigrations(db: Database.Database): void {
+  const migrationsDir = path.resolve(__dirname, '../../drizzle');
+  const files = fs.readdirSync(migrationsDir).filter(f => f.endsWith('.sql')).sort();
+  for (const f of files) {
+    const sql = fs.readFileSync(path.join(migrationsDir, f), 'utf8');
+    const statements = sql.split(/-->\s*statement-breakpoint/);
+    for (const stmt of statements) {
+      const clean = stmt.trim();
+      if (clean) db.exec(clean);
+    }
+  }
+}
+
+async function importSUT() {
+  return await import('./federation.js');
+}
+
+async function importManager() {
+  const mod = await import('../ws/handler.js');
+  return mod.connectionManager;
+}
+
+let sqlite: Database.Database;
+
+/** Insert a minimal native user row so dmMembers FK constraints pass. */
+function seedUser(id: string): void {
+  testDb.insert(schema.users).values({
+    id,
+    username: id,
+    passwordHash: '!test',
+    createdAt: Date.now(),
+  }).run();
+}
+
+describe('processRelayEvents → processDmCallStartEvent', () => {
+  beforeEach(async () => {
+    sqlite = new Database(':memory:');
+    testDb = drizzle(sqlite, { schema });
+    applyMigrations(sqlite);
+
+    const cm = await importManager();
+    for (const [fedId] of cm.getAllFederatedCalls()) cm.clearFederatedCall(fedId);
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    sqlite.close();
+  });
+
+  it('Path B: zero matches → undeliverable, no FederatedCallEntry created', async () => {
+    // Arrange: no local DM, no local user matching the participant list
+    const { processRelayEvents } = await importSUT();
+    const cm = await importManager();
+
+    const federatedId = 'fed-call-pathB-empty';
+    const event = {
+      eventType: 'dm_call_start' as const,
+      messageId: 'msg-1',
+      encryptionVersion: 0 as const,
+      timestamp: Date.now(),
+      federatedId,
+      call: {
+        livekitUrl: 'wss://lk.example',
+        tokens: { 'caller-home': 'tok-c', 'unknown-home': 'tok-u' },
+        caller: {
+          homeUserId: 'caller-home',
+          homeInstance: 'https://remote.example',
+          displayName: 'Caller',
+        },
+        participants: [
+          { homeUserId: 'caller-home', homeInstance: 'https://remote.example', displayName: 'Caller' },
+          { homeUserId: 'unknown-home', homeInstance: 'https://remote.example', displayName: 'Unknown' },
+        ],
+      },
+    };
+
+    // Act
+    const result = await processRelayEvents([event], 'https://remote.example', 'https://remote.example', testDb);
+
+    // Assert
+    expect(result.accepted).toEqual([]);
+    expect(result.rejected).toEqual([]);
+    expect(result.undeliverable).toEqual([
+      { messageId: 'msg-1', reason: 'no_recipient' },
+    ]);
+    expect(cm.getFederatedCall(federatedId)).toBeUndefined();
+  });
+
+  it('Path A: zero connected local members → undeliverable, no entry created', async () => {
+    const { processRelayEvents } = await importSUT();
+    const cm = await importManager();
+
+    // Arrange: local DM channel with federated_id matches; two local members, both offline
+    const federatedId = 'fed-call-pathA-all-offline';
+    const dmChannelId = 'dm-1';
+    seedUser('bob-local');
+    seedUser('alice-local');
+    testDb.insert(schema.dmChannels).values({
+      id: dmChannelId,
+      ownerId: null,
+      federatedId,
+      createdAt: Date.now(),
+    }).run();
+    testDb.insert(schema.dmMembers).values([
+      { dmChannelId, userId: 'bob-local' },
+      { dmChannelId, userId: 'alice-local' },
+    ]).run();
+
+    // Stub: both users offline (zero WS connections)
+    vi.spyOn(cm, 'getUserConnections').mockImplementation(() => new Set());
+
+    const event = {
+      eventType: 'dm_call_start' as const,
+      messageId: 'msg-2',
+      encryptionVersion: 0 as const,
+      timestamp: Date.now(),
+      federatedId,
+      call: {
+        livekitUrl: 'wss://lk.example',
+        tokens: {
+          'caller-home': 'tok-c',
+          'bob-local': 'tok-b',
+          'alice-local': 'tok-a',
+        },
+        caller: {
+          homeUserId: 'caller-home',
+          homeInstance: 'https://remote.example',
+          displayName: 'Caller',
+        },
+        participants: [],
+      },
+    };
+
+    const sendToUserSpy = vi.spyOn(cm, 'sendToUser');
+
+    const result = await processRelayEvents([event], 'https://remote.example', 'https://remote.example', testDb);
+
+    expect(result.accepted).toEqual([]);
+    expect(result.undeliverable).toEqual([{ messageId: 'msg-2', reason: 'no_recipient' }]);
+    // No dm_call_incoming dispatched to anyone
+    expect(sendToUserSpy).not.toHaveBeenCalledWith(
+      expect.any(String),
+      expect.objectContaining({ type: 'dm_call_incoming' }),
+    );
+    // No FederatedCallEntry
+    expect(cm.getFederatedCall(federatedId)).toBeUndefined();
+  });
+
+  it('Path A: mixed online + offline rings only connected members', async () => {
+    const { processRelayEvents } = await importSUT();
+    const cm = await importManager();
+
+    const federatedId = 'fed-call-pathA-mixed';
+    const dmChannelId = 'dm-2';
+    seedUser('bob-local');
+    seedUser('carol-local');
+    testDb.insert(schema.dmChannels).values({
+      id: dmChannelId,
+      ownerId: null,
+      federatedId,
+      createdAt: Date.now(),
+    }).run();
+    testDb.insert(schema.dmMembers).values([
+      { dmChannelId, userId: 'bob-local' },
+      { dmChannelId, userId: 'carol-local' },
+    ]).run();
+
+    // Bob online, Carol offline
+    vi.spyOn(cm, 'getUserConnections').mockImplementation((uid: string) =>
+      uid === 'bob-local' ? new Set(['fakews' as unknown as WebSocket]) : new Set(),
+    );
+
+    const sendToUserSpy = vi.spyOn(cm, 'sendToUser');
+
+    const event = {
+      eventType: 'dm_call_start' as const,
+      messageId: 'msg-3',
+      encryptionVersion: 0 as const,
+      timestamp: Date.now(),
+      federatedId,
+      call: {
+        livekitUrl: 'wss://lk.example',
+        tokens: {
+          'caller-home': 'tok-c',
+          'bob-local': 'tok-b',
+          'carol-local': 'tok-car',
+        },
+        caller: {
+          homeUserId: 'caller-home',
+          homeInstance: 'https://remote.example',
+          displayName: 'Caller',
+        },
+        participants: [],
+      },
+    };
+
+    const result = await processRelayEvents([event], 'https://remote.example', 'https://remote.example', testDb);
+
+    expect(result.accepted).toEqual(['msg-3']);
+    expect(result.undeliverable).toEqual([]);
+
+    // Bob was rung
+    expect(sendToUserSpy).toHaveBeenCalledWith(
+      'bob-local',
+      expect.objectContaining({ type: 'dm_call_incoming', livekitToken: 'tok-b' }),
+    );
+    // Carol was NOT rung (offline)
+    expect(sendToUserSpy).not.toHaveBeenCalledWith(
+      'carol-local',
+      expect.anything(),
+    );
+
+    const entry = cm.getFederatedCall(federatedId);
+    expect(entry).toBeDefined();
+    expect(entry!.ringedUserIds).toEqual(['bob-local']);
+  });
+});
diff --git a/packages/server/src/routes/federation.ts b/packages/server/src/routes/federation.ts
index 6ded4e4f..b14a9121 100644
--- a/packages/server/src/routes/federation.ts
+++ b/packages/server/src/routes/federation.ts
@@ -1532,7 +1532,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
       }
 
       // 3. Process each event
-      const { accepted, rejected } = await processRelayEvents(body.events, sourceInstance, peer.origin, db);
+      const { accepted, rejected, undeliverable } = await processRelayEvents(body.events, sourceInstance, peer.origin, db);
 
       // 4. Update peer status
       db.update(schema.federationPeers)
@@ -1555,6 +1555,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
         accepted,
         rejected,
         maxUploadSize: settings?.maxUploadSizeBytes ?? config.maxUploadSize,
+        ...(undeliverable.length > 0 ? { undeliverable } : {}),
       };
 
       return reply.code(200).send(response);
@@ -2066,9 +2067,14 @@ export async function processRelayEvents(
   sourceInstance: string,
   peerOrigin: string,
   db: ReturnType<typeof getDb>,
-): Promise<{ accepted: string[]; rejected: Array<{ messageId: string; reason: string }> }> {
+): Promise<{
+  accepted: string[];
+  rejected: Array<{ messageId: string; reason: string }>;
+  undeliverable: Array<{ messageId: string; reason: string }>;
+}> {
   const accepted: string[] = [];
   const rejected: Array<{ messageId: string; reason: string }> = [];
+  const undeliverable: Array<{ messageId: string; reason: string }> = [];
 
   for (const event of events) {
     try {
@@ -2116,7 +2122,7 @@ export async function processRelayEvents(
           processFileRejectedEvent(event, sourceInstance, db, accepted, rejected);
           break;
         case 'dm_call_start':
-          processDmCallStartEvent(event, sourceInstance, db, accepted, rejected);
+          processDmCallStartEvent(event, sourceInstance, db, accepted, rejected, undeliverable);
           break;
         case 'dm_call_accept':
           processDmCallAcceptEvent(event, sourceInstance, db, accepted, rejected);
@@ -2156,7 +2162,7 @@ export async function processRelayEvents(
     }
   }
 
-  return { accepted, rejected };
+  return { accepted, rejected, undeliverable };
 }
 
 // ─── Helpers ────────────────────────────────────────────────────────────────
@@ -4253,6 +4259,7 @@ function processDmCallStartEvent(
   db: ReturnType<typeof getDb>,
   accepted: string[],
   rejected: Array<{ messageId: string; reason: string }>,
+  undeliverable: Array<{ messageId: string; reason: string }>,
 ): void {
   if (!event.call?.caller || !event.call.livekitUrl || !event.call.tokens || !event.federatedId) {
     rejected.push({ messageId: event.messageId, reason: 'missing_call_payload' });
@@ -4305,6 +4312,11 @@ function processDmCallStartEvent(
       // Bug 1 fix: don't ring the caller on this instance
       if (homeUserId === event.call.caller.homeUserId) continue;
 
+      // #18: skip offline members. Entry-vs-no-entry decision uses the same
+      // connection-count signal Path B has always used — keeps the two paths
+      // symmetric in what counts as "ringed."
+      if (connectionManager.getUserConnections(member.userId).size === 0) continue;
+
       const token = event.call!.tokens![homeUserId];
       connectionManager.sendToUser(member.userId, {
         type: 'dm_call_incoming',
@@ -4319,6 +4331,14 @@ function processDmCallStartEvent(
       ringedUserIds.push(member.userId);
     }
 
+    if (ringedUserIds.length === 0) {
+      // #18: no local member was reachable. Do not create a FederatedCallEntry
+      // (it would strand with no accept/reject path); surface to the caller
+      // via undeliverable so it can tear down its ring room instead of hanging.
+      undeliverable.push({ messageId: event.messageId, reason: 'no_recipient' });
+      return;
+    }
+
     const entry: FederatedCallEntry = {
       dmChannelId: localDmChannelId,
       federatedId: event.federatedId,
@@ -4395,8 +4415,11 @@ function processDmCallStartEvent(
     }
 
     if (ringedUserIds.length === 0) {
-      // No connected users found — silently accept (not an error)
-      accepted.push(event.messageId);
+      // No recipient reachable — signal to caller via third ack bucket (#18).
+      // The remote processed the event cleanly; this is not a data error, but
+      // the caller must learn that nobody was rung so it can tear down its
+      // local ring room instead of hanging 60s waiting for an accept.
+      undeliverable.push({ messageId: event.messageId, reason: 'no_recipient' });
       return;
     }
 
diff --git a/packages/server/src/utils/federationOutbox.ts b/packages/server/src/utils/federationOutbox.ts
index 57aad54d..b078f438 100644
--- a/packages/server/src/utils/federationOutbox.ts
+++ b/packages/server/src/utils/federationOutbox.ts
@@ -524,7 +524,15 @@ export type CallRelayFailureReason =
   | 'post_failed';
 
 export type CallRelayResult =
-  | { ok: true }
+  | {
+      ok: true;
+      /**
+       * messageIds the remote reported as undeliverable (remote processed the
+       * event cleanly but had no reachable recipient). Empty array for old
+       * peers that don't set `undeliverable` on FederationRelayResponse.
+       */
+      undeliverable: string[];
+    }
   | { ok: false; reason: CallRelayFailureReason; error: string };
 
 /** Per-peer failure record returned by Path-1 call fan-out helpers. */
@@ -631,7 +639,26 @@ export async function sendCallRelay(
       signal: AbortSignal.timeout(10_000),
     });
 
-    if (res.ok) return { ok: true };
+    if (res.ok) {
+      // Parse response body to surface the undeliverable bucket. Old peers
+      // omit the field; treat as empty. Body shape: FederationRelayResponse.
+      let undeliverable: string[] = [];
+      try {
+        const responseBody = (await res.json()) as { undeliverable?: unknown };
+        if (Array.isArray(responseBody.undeliverable)) {
+          undeliverable = responseBody.undeliverable
+            .filter((u): u is { messageId: string } =>
+              typeof u === 'object' && u !== null && typeof (u as { messageId?: unknown }).messageId === 'string',
+            )
+            .map(u => u.messageId);
+        } else if (responseBody.undeliverable !== undefined) {
+          console.warn('[federation] sendCallRelay: peer returned non-array undeliverable, ignoring:', targetPeerOrigin);
+        }
+      } catch (err) {
+        console.debug('[federation] sendCallRelay: response body unparseable, treating as old-format:', targetPeerOrigin, err);
+      }
+      return { ok: true, undeliverable };
+    }
 
     const text = await res.text().catch(() => '');
     if (res.status >= 400 && res.status < 500) {
diff --git a/packages/server/src/utils/federationOutbox.undeliverable.test.ts b/packages/server/src/utils/federationOutbox.undeliverable.test.ts
new file mode 100644
index 00000000..8a3cdb4b
--- /dev/null
+++ b/packages/server/src/utils/federationOutbox.undeliverable.test.ts
@@ -0,0 +1,133 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { drizzle } from 'drizzle-orm/better-sqlite3';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import * as schema from '../db/schema.js';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+type TestDb = ReturnType<typeof drizzle<typeof schema>>;
+let testDb: TestDb;
+
+vi.mock('../db/index.js', () => ({
+  getDb: () => testDb,
+  schema,
+}));
+
+vi.mock('./federationAuth.js', async () => {
+  const actual = await vi.importActual<typeof import('./federationAuth.js')>('./federationAuth.js');
+  return {
+    ...actual,
+    getOurOrigin: () => 'https://local.example',
+    buildFederationHeaders: () => ({}),
+  };
+});
+
+function applyMigrations(db: Database.Database): void {
+  const migrationsDir = path.resolve(__dirname, '../../drizzle');
+  const files = fs.readdirSync(migrationsDir).filter(f => f.endsWith('.sql')).sort();
+  for (const f of files) {
+    const sql = fs.readFileSync(path.join(migrationsDir, f), 'utf8');
+    const statements = sql.split(/-->\s*statement-breakpoint/);
+    for (const stmt of statements) {
+      const clean = stmt.trim();
+      if (clean) db.exec(clean);
+    }
+  }
+}
+
+function seedActivePeer(origin: string): void {
+  testDb.insert(schema.federationPeers).values({
+    id: `peer-${origin}`,
+    origin,
+    hmacSecret: 'secret',
+    status: 'active',
+    instanceName: 'Peer',
+    lastSyncedAt: 0,
+    createdAt: Date.now(),
+  }).run();
+}
+
+let sqlite: Database.Database;
+
+describe('sendCallRelay response shape', () => {
+  beforeEach(() => {
+    sqlite = new Database(':memory:');
+    testDb = drizzle(sqlite, { schema });
+    applyMigrations(sqlite);
+    seedActivePeer('https://peer.example');
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    sqlite.close();
+  });
+
+  const baseEvent = {
+    eventType: 'dm_call_start' as const,
+    messageId: 'msg-X',
+    encryptionVersion: 0 as const,
+    timestamp: Date.now(),
+    federatedId: 'fed-X',
+    call: {
+      livekitUrl: 'wss://lk.example',
+      tokens: {},
+      caller: { homeUserId: 'c', homeInstance: 'https://local.example', displayName: 'C' },
+      participants: [],
+    },
+  };
+
+  it('returns {ok:true, undeliverable:[]} when remote omits the field', async () => {
+    vi.stubGlobal('fetch', vi.fn(async () =>
+      new Response(JSON.stringify({ accepted: ['msg-X'], rejected: [], maxUploadSize: 1000 }), {
+        status: 200,
+        headers: { 'content-type': 'application/json' },
+      }),
+    ));
+
+    const { sendCallRelay } = await import('./federationOutbox.js');
+    const result = await sendCallRelay('https://peer.example', [baseEvent]);
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.undeliverable).toEqual([]);
+    }
+  });
+
+  it('returns {ok:true, undeliverable:["msg-X"]} when remote lists it', async () => {
+    vi.stubGlobal('fetch', vi.fn(async () =>
+      new Response(JSON.stringify({
+        accepted: [],
+        rejected: [],
+        undeliverable: [{ messageId: 'msg-X', reason: 'no_recipient' }],
+        maxUploadSize: 1000,
+      }), {
+        status: 200,
+        headers: { 'content-type': 'application/json' },
+      }),
+    ));
+
+    const { sendCallRelay } = await import('./federationOutbox.js');
+    const result = await sendCallRelay('https://peer.example', [baseEvent]);
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.undeliverable).toEqual(['msg-X']);
+    }
+  });
+
+  it('failure shape unchanged on HTTP 5xx', async () => {
+    vi.stubGlobal('fetch', vi.fn(async () =>
+      new Response('server down', { status: 503 }),
+    ));
+
+    const { sendCallRelay } = await import('./federationOutbox.js');
+    const result = await sendCallRelay('https://peer.example', [baseEvent]);
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.reason).toBe('peer_transient_failure');
+    }
+  });
+});
diff --git a/packages/server/src/utils/federationPeerActivation.test.ts b/packages/server/src/utils/federationPeerActivation.test.ts
index f8127a37..2b5747c4 100644
--- a/packages/server/src/utils/federationPeerActivation.test.ts
+++ b/packages/server/src/utils/federationPeerActivation.test.ts
@@ -32,7 +32,7 @@ vi.mock('../utils/federationAuth.js', () => ({
 }));
 
 vi.mock('../routes/federation.js', () => ({
-  processRelayEvents: vi.fn().mockResolvedValue({ accepted: [], rejected: [] }),
+  processRelayEvents: vi.fn().mockResolvedValue({ accepted: [], rejected: [], undeliverable: [] }),
 }));
 
 vi.mock('../ws/handler.js', () => ({
diff --git a/packages/server/src/ws/events.callStartUndeliverable.test.ts b/packages/server/src/ws/events.callStartUndeliverable.test.ts
new file mode 100644
index 00000000..4293a7c6
--- /dev/null
+++ b/packages/server/src/ws/events.callStartUndeliverable.test.ts
@@ -0,0 +1,259 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { drizzle } from 'drizzle-orm/better-sqlite3';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import * as schema from '../db/schema.js';
+import { setWorkerId } from '../utils/snowflake.js';
+
+setWorkerId(1);
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+type TestDb = ReturnType<typeof drizzle<typeof schema>>;
+let testDb: TestDb;
+
+vi.mock('../db/index.js', () => ({
+  getDb: () => testDb,
+  schema,
+}));
+
+vi.mock('../utils/federationAuth.js', async () => {
+  const actual = await vi.importActual<typeof import('../utils/federationAuth.js')>(
+    '../utils/federationAuth.js',
+  );
+  return {
+    ...actual,
+    getOurOrigin: () => 'https://local.example',
+    buildFederationHeaders: () => ({}),
+    generateFederatedCallToken: () => Promise.resolve('fake-token'),
+  };
+});
+
+// Mock sendCallRelay so the test controls relay results per peer. The
+// implementation captures the messageId each call was made with so tests
+// can return { undeliverable: [messageId] } dynamically.
+type RelayArgs = [string, Array<{ messageId: string }>];
+const sendCallRelayMock = vi.fn();
+vi.mock('../utils/federationOutbox.js', async () => {
+  const actual = await vi.importActual<typeof import('../utils/federationOutbox.js')>(
+    '../utils/federationOutbox.js',
+  );
+  return {
+    ...actual,
+    sendCallRelay: (...args: RelayArgs) => sendCallRelayMock(...args),
+  };
+});
+
+// Mock config to claim LiveKit is configured.
+vi.mock('../config.js', async () => {
+  const actual = await vi.importActual<typeof import('../config.js')>('../config.js');
+  return {
+    ...actual,
+    config: {
+      ...actual.config,
+      domain: 'local.example',
+      livekit: {
+        url: 'wss://local.example/livekit',
+        apiKey: 'key',
+        apiSecret: 'secret',
+      },
+    },
+  };
+});
+
+function applyMigrations(db: Database.Database): void {
+  const migrationsDir = path.resolve(__dirname, '../../drizzle');
+  const files = fs.readdirSync(migrationsDir).filter(f => f.endsWith('.sql')).sort();
+  for (const f of files) {
+    const sql = fs.readFileSync(path.join(migrationsDir, f), 'utf8');
+    const statements = sql.split(/-->\s*statement-breakpoint/);
+    for (const stmt of statements) {
+      const clean = stmt.trim();
+      if (clean) db.exec(clean);
+    }
+  }
+}
+
+function seedActivePeer(origin: string, instanceName: string): void {
+  testDb.insert(schema.federationPeers).values({
+    id: `peer-${origin}`,
+    origin,
+    hmacSecret: 'secret',
+    status: 'active',
+    instanceName,
+    lastSyncedAt: 0,
+    createdAt: Date.now(),
+  }).run();
+}
+
+function seedLocalUser(id: string, opts: { homeUserId?: string | null; homeInstance?: string | null } = {}): void {
+  testDb.insert(schema.users).values({
+    id,
+    username: id,
+    passwordHash: 'test',
+    homeUserId: opts.homeUserId ?? null,
+    homeInstance: opts.homeInstance ?? null,
+    createdAt: Date.now(),
+  }).run();
+}
+
+function seedDmChannel(id: string, federatedId: string, ownerId: string | null): void {
+  testDb.insert(schema.dmChannels).values({
+    id,
+    ownerId,
+    federatedId,
+    createdAt: Date.now(),
+  }).run();
+}
+
+function seedDmMember(dmChannelId: string, userId: string): void {
+  testDb.insert(schema.dmMembers).values({ dmChannelId, userId }).run();
+}
+
+async function importSUT() {
+  return await import('./events.js');
+}
+
+async function importManager() {
+  return (await import('./handler.js')).connectionManager;
+}
+
+let sqlite: Database.Database;
+
+describe('sendFederatedCallStart — undeliverable reclassification (#18)', () => {
+  beforeEach(async () => {
+    sqlite = new Database(':memory:');
+    testDb = drizzle(sqlite, { schema });
+    applyMigrations(sqlite);
+
+    const cm = await importManager();
+    // Reset federatedCalls + rooms between tests.
+    for (const [fedId] of cm.getAllFederatedCalls()) cm.clearFederatedCall(fedId);
+    sendCallRelayMock.mockReset();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    sqlite.close();
+  });
+
+  it('single targeted peer returns undeliverable → terminal dm_call_undeliverable, room destroyed', async () => {
+    // 1-on-1 DM: Alice local, Bob remote on orbit.
+    const federatedId = 'fed-1on1';
+    seedLocalUser('alice', { homeUserId: null, homeInstance: null });
+    seedLocalUser('bob-stub', { homeUserId: 'bob-home', homeInstance: 'https://orbit.example' });
+    seedDmChannel('dm-1', federatedId, null);
+    seedDmMember('dm-1', 'alice');
+    seedDmMember('dm-1', 'bob-stub');
+    seedActivePeer('https://orbit.example', 'Orbit');
+
+    const cm = await importManager();
+    cm.createDmRoom('dm-1', 'alice');  // caller's local ring room (mirrors real flow)
+
+    // Capture the messageId sendFederatedCallStart generates, return it as undeliverable.
+    sendCallRelayMock.mockImplementation(async (_origin: string, events: Array<{ messageId: string }>) => {
+      return { ok: true, undeliverable: [events[0]!.messageId] };
+    });
+
+    const sendToUserSpy = vi.spyOn(cm, 'sendToUser');
+    const destroyRoomSpy = vi.spyOn(cm, 'destroyRoom');
+
+    const { sendFederatedCallStartForTest } = await importSUT();
+    await sendFederatedCallStartForTest('dm-1', 'alice', 'Alice');
+
+    // The caller (Alice) got a terminal dm_call_undeliverable with reason='no_recipient'.
+    const undelivCalls = sendToUserSpy.mock.calls.filter(([, ev]) =>
+      (ev as { type: string }).type === 'dm_call_undeliverable',
+    );
+    expect(undelivCalls).toHaveLength(1);
+    expect(undelivCalls[0]![0]).toBe('alice');
+
+    const ev = undelivCalls[0]![1] as {
+      terminal: boolean;
+      phase: string;
+      failures: Array<{ reason: string; peerLabel?: string; peerOrigin?: string }>;
+    };
+    expect(ev.terminal).toBe(true);
+    expect(ev.phase).toBe('start');
+    expect(ev.failures).toHaveLength(1);
+    expect(ev.failures[0]!.reason).toBe('no_recipient');
+    expect(ev.failures[0]!.peerOrigin).toBe('https://orbit.example');
+    expect(ev.failures[0]!.peerLabel).toBe('Orbit');
+
+    // Room was destroyed.
+    expect(destroyRoomSpy).toHaveBeenCalledWith('dm-1');
+  });
+
+  it('group DM mixed delivered + undeliverable → non-terminal, failures lists only the undeliverable peer', async () => {
+    // Group DM: caller + one member on orbit (delivers) + one member on nova (undeliverable).
+    const federatedId = 'fed-group';
+    seedLocalUser('alice', { homeUserId: null, homeInstance: null });
+    seedLocalUser('bob-stub', { homeUserId: 'bob-home', homeInstance: 'https://orbit.example' });
+    seedLocalUser('carol-stub', { homeUserId: 'carol-home', homeInstance: 'https://nova.example' });
+    seedDmChannel('dm-group', federatedId, 'alice');  // group DM: ownerId non-null
+    seedDmMember('dm-group', 'alice');
+    seedDmMember('dm-group', 'bob-stub');
+    seedDmMember('dm-group', 'carol-stub');
+    seedActivePeer('https://orbit.example', 'Orbit');
+    seedActivePeer('https://nova.example', 'Nova');
+
+    const cm = await importManager();
+    cm.createDmRoom('dm-group', 'alice');
+
+    // Orbit delivers (empty undeliverable), Nova returns messageId in undeliverable.
+    sendCallRelayMock.mockImplementation(async (origin: string, events: Array<{ messageId: string }>) => {
+      if (origin === 'https://nova.example') {
+        return { ok: true, undeliverable: [events[0]!.messageId] };
+      }
+      return { ok: true, undeliverable: [] };
+    });
+
+    const sendToUserSpy = vi.spyOn(cm, 'sendToUser');
+    const destroyRoomSpy = vi.spyOn(cm, 'destroyRoom');
+
+    const { sendFederatedCallStartForTest } = await importSUT();
+    await sendFederatedCallStartForTest('dm-group', 'alice', 'Alice');
+
+    // Room NOT destroyed (orbit delivered).
+    expect(destroyRoomSpy).not.toHaveBeenCalledWith('dm-group');
+
+    const undelivCalls = sendToUserSpy.mock.calls.filter(([uid, ev]) =>
+      uid === 'alice' && (ev as { type: string }).type === 'dm_call_undeliverable',
+    );
+    expect(undelivCalls).toHaveLength(1);
+
+    const ev = undelivCalls[0]![1] as {
+      terminal: boolean;
+      failures: Array<{ reason: string; peerOrigin?: string }>;
+    };
+    expect(ev.terminal).toBe(false);
+    expect(ev.failures).toHaveLength(1);
+    expect(ev.failures[0]!.reason).toBe('no_recipient');
+    expect(ev.failures[0]!.peerOrigin).toBe('https://nova.example');
+  });
+
+  it('single targeted peer delivers (empty undeliverable) → no undeliverable event', async () => {
+    const federatedId = 'fed-happy';
+    seedLocalUser('alice', {});
+    seedLocalUser('bob-stub', { homeUserId: 'bob-home', homeInstance: 'https://orbit.example' });
+    seedDmChannel('dm-happy', federatedId, null);
+    seedDmMember('dm-happy', 'alice');
+    seedDmMember('dm-happy', 'bob-stub');
+    seedActivePeer('https://orbit.example', 'Orbit');
+
+    const cm = await importManager();
+    cm.createDmRoom('dm-happy', 'alice');
+
+    sendCallRelayMock.mockResolvedValue({ ok: true, undeliverable: [] });
+
+    const sendToUserSpy = vi.spyOn(cm, 'sendToUser');
+    const { sendFederatedCallStartForTest } = await importSUT();
+    await sendFederatedCallStartForTest('dm-happy', 'alice', 'Alice');
+
+    const undelivCalls = sendToUserSpy.mock.calls.filter(([, ev]) =>
+      (ev as { type: string }).type === 'dm_call_undeliverable',
+    );
+    expect(undelivCalls).toHaveLength(0);
+  });
+});
diff --git a/packages/server/src/ws/events.dmCallRelay.test.ts b/packages/server/src/ws/events.dmCallRelay.test.ts
index 26547070..aae10a6e 100644
--- a/packages/server/src/ws/events.dmCallRelay.test.ts
+++ b/packages/server/src/ws/events.dmCallRelay.test.ts
@@ -144,7 +144,7 @@ describe('handleDmCallEnd Path-2 relay failure', () => {
     const fedCall = makeFedCall({ state: 'active' });
     connectionManager.createFederatedCall(fedCall);
     const sendToUserSpy = vi.spyOn(connectionManager, 'sendToUser');
-    sendCallRelayMock.mockResolvedValue({ ok: true });
+    sendCallRelayMock.mockResolvedValue({ ok: true, undeliverable: [] });
 
     await handleDmCallEndForTest(
       { federatedCallId: fedCall.federatedId },
@@ -191,7 +191,7 @@ describe('handleDmCallReject Path-2 relay failure', () => {
     const fedCall = makeFedCall();
     connectionManager.createFederatedCall(fedCall);
     const sendToUserSpy = vi.spyOn(connectionManager, 'sendToUser');
-    sendCallRelayMock.mockResolvedValue({ ok: true });
+    sendCallRelayMock.mockResolvedValue({ ok: true, undeliverable: [] });
 
     await handleDmCallRejectForTest(
       { federatedCallId: fedCall.federatedId },
@@ -282,7 +282,7 @@ describe('handleDmCallAccept Path-2 relay failure', () => {
     const fedCall = makeFedCall();
     connectionManager.createFederatedCall(fedCall);
     const sendToUserSpy = vi.spyOn(connectionManager, 'sendToUser');
-    sendCallRelayMock.mockResolvedValue({ ok: true });
+    sendCallRelayMock.mockResolvedValue({ ok: true, undeliverable: [] });
 
     await handleDmCallAcceptForTest(
       { federatedCallId: fedCall.federatedId },
diff --git a/packages/server/src/ws/events.ts b/packages/server/src/ws/events.ts
index 61955143..6aaa859c 100644
--- a/packages/server/src/ws/events.ts
+++ b/packages/server/src/ws/events.ts
@@ -1925,10 +1925,24 @@ async function sendFederatedCallStart(
   }
 
   // ─── Targeted relay: fan out in parallel, await results ────────────────────
+  // Each peer's result has THREE possible classifications:
+  //   ok=true, messageId NOT in undeliverable → delivered
+  //   ok=true, messageId IN undeliverable     → new: no_recipient failure (#18)
+  //   ok=false                                → existing failure reasons
   const targetedResults = await Promise.all(
     Array.from(targetedPeers.keys()).map(async peerOrigin => {
-      const result = await sendCallRelay(peerOrigin, [buildRelayEvent()]);
+      const relayEvent = buildRelayEvent();
+      const result = await sendCallRelay(peerOrigin, [relayEvent]);
       if (result.ok) {
+        if (result.undeliverable.includes(relayEvent.messageId)) {
+          console.warn(`[federation] dm_call_start to ${peerOrigin}: remote had no recipient`);
+          return {
+            origin: peerOrigin,
+            ok: false as const,
+            reason: 'no_recipient' as const satisfies DmCallUndeliverableReason,
+            error: 'remote reported no_recipient',
+          };
+        }
         return { origin: peerOrigin, ok: true as const };
       }
       const reason = mapCallReasonToEventReason(result.reason);
@@ -2483,3 +2497,4 @@ export function registerCallRelayHooks(): void {
 export const handleDmCallAcceptForTest = handleDmCallAccept;
 export const handleDmCallRejectForTest = handleDmCallReject;
 export const handleDmCallEndForTest = handleDmCallEnd;
+export const sendFederatedCallStartForTest = sendFederatedCallStart;
diff --git a/packages/shared/src/types.ts b/packages/shared/src/types.ts
index e5dae5cc..29faa8ec 100644
--- a/packages/shared/src/types.ts
+++ b/packages/shared/src/types.ts
@@ -362,7 +362,8 @@ export type DmCallUndeliverableReason =
   | 'peer_rejected'
   | 'peer_awaiting_approval'
   | 'peer_transient_failure'
-  | 'livekit_unavailable';
+  | 'livekit_unavailable'
+  | 'no_recipient';
 
 export type DmCallPhase = 'start' | 'accept' | 'reject' | 'end' | 'host_unreachable';
 
@@ -967,6 +968,14 @@ export interface FederationRelayRequest {
 export interface FederationRelayResponse {
   accepted: string[];
   rejected: Array<{ messageId: string; reason: string }>;
+  /**
+   * Third classification (additive, v1.x): events that were processed cleanly
+   * but had no reachable recipient. Distinct from `rejected` (data/protocol
+   * refusal). Currently used only for `dm_call_start` — other event types
+   * keep accepted/rejected semantics unchanged. Omitted when empty for
+   * wire-size hygiene and byte-identical responses in the typical case.
+   */
+  undeliverable?: Array<{ messageId: string; reason: string }>;
   maxUploadSize: number;
 }
 
diff --git a/packages/web/src/hooks/__tests__/useWebSocket.callUndeliverable.test.ts b/packages/web/src/hooks/__tests__/useWebSocket.callUndeliverable.test.ts
index 2a3c9840..f6ef623e 100644
--- a/packages/web/src/hooks/__tests__/useWebSocket.callUndeliverable.test.ts
+++ b/packages/web/src/hooks/__tests__/useWebSocket.callUndeliverable.test.ts
@@ -54,4 +54,40 @@ describe('buildCallUndeliverableToast', () => {
     expect(msg.toLowerCase()).toContain('orbit');
     expect(msg.toLowerCase()).toContain('peered');
   });
+
+  it('renders no_recipient single-failure terminal copy', () => {
+    const fail = (peerLabel = 'Orbit') => ({
+      reason: 'no_recipient',
+      peerOrigin: 'https://orbit.local',
+      peerLabel,
+    });
+    expect(buildCallUndeliverableToast([fail()], true, 'start'))
+      .toBe("Orbit couldn't ring anyone.");
+  });
+
+  it('no_recipient falls back to origin when peerLabel missing', () => {
+    const fail = {
+      reason: 'no_recipient',
+      peerOrigin: 'https://orbit.local',
+    };
+    expect(buildCallUndeliverableToast([fail], true, 'start'))
+      .toMatch(/orbit\.local couldn't ring anyone\./);
+  });
+
+  it('no_recipient in a multi-failure terminal falls back to multi-instance copy', () => {
+    const failures = [
+      { reason: 'no_recipient', peerOrigin: 'https://orbit.local', peerLabel: 'Orbit' },
+      { reason: 'peer_transient_failure', peerOrigin: 'https://nova.local', peerLabel: 'Nova' },
+    ];
+    expect(buildCallUndeliverableToast(failures, true, 'start'))
+      .toMatch(/Could not reach 2 instances: Orbit, Nova/);
+  });
+
+  it('no_recipient non-terminal uses the existing "Some participants" line', () => {
+    const failures = [
+      { reason: 'no_recipient', peerOrigin: 'https://orbit.local', peerLabel: 'Orbit' },
+    ];
+    expect(buildCallUndeliverableToast(failures, false, 'start'))
+      .toMatch(/Some participants could not be reached: Orbit/);
+  });
 });
diff --git a/packages/web/src/utils/callUndeliverableToast.ts b/packages/web/src/utils/callUndeliverableToast.ts
index dd4aeefc..47060e78 100644
--- a/packages/web/src/utils/callUndeliverableToast.ts
+++ b/packages/web/src/utils/callUndeliverableToast.ts
@@ -76,6 +76,8 @@ export function buildCallUndeliverableToast(
       return `Could not reach ${label}. Try again in a moment.`;
     case 'livekit_unavailable':
       return 'Voice is not configured on this instance.';
+    case 'no_recipient':
+      return `${label} couldn't ring anyone.`;
     default:
       return `Call to ${label} could not be placed.`;
   }