diff --git a/CHANGELOG.md b/CHANGELOG.md
index 56be3d03..95ca99ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 - **RdClient desktop — native Cliprdr + folder file transfer stack (Refs #350):** recovered onto current `dev` from divergent history — Tauri `desktop_*` / `desktop_clipboard_*` IPC, `cliprdr.js`, desktop DnD, streamed folder upload/download. Requires rebuilt `rdclient-desktop` **and** panel update.
 
 ### Fixed
+- **Outbound “ID does not exist” after 3.5.16 (#302 residual):** stock RustDesk PunchHole/RequestRelay on a new TCP port (no login token, no shared RegisterPk session) was rejected as `initiator_not_registered` because 3.5.16 removed the safe `FindAllByIP` fallback restored in 3.5.15. Auth again authorizes when exactly one live peer shares the public IP; multiple live peers at that IP still refuse with `initiator_ambiguous_same_nat` (no identity inheritance). Ships via panel update (Go signal restart). Verify: stock client connect no longer shows “ID does not exist” when the initiator is the sole live peer at its public IP.
 - **Relay `Unauthorized relay UUID` after P2P fallback (#356):** when hole punch timed out and the target sent `RelayResponse`, signal forwarded the UUID without minting a relay ticket, so hbbr rejected both peers (`Reset by the peer(0)`). `handleRelayResponseForward` now authorizes the initiator/target pair before advertising the UUID (same ticket path as `RequestRelay`). Ships via panel update (Go signal/relay restart). Verify: connection that needs relay after P2P timeout succeeds; no `[relay] Unauthorized relay UUID` for that session.
 - **RdClient desktop — Copy-Paste / File Transfer creates 0KB empty remote files (#350):** Tauri IPC returns file chunks as base64 strings; JS treated them as `Uint8Array` constructors (`new Uint8Array(base64String)`), which always yields length 0, so Cliprdr and the File Transfer modal wrote empty remote files. `coerceBinaryPayload` now decodes base64 before upload/Cliprdr paths. Ships via panel update (`local-files.js` / `filetransfer.js` / `cliprdr.js` / `compress.js` / `protocol.js`).
 - **RdClient desktop — Cliprdr paste still 0KB after base64 coerce (#350):** outbound FILEGROUPDESCRIPTOR advertised `FD_FILESIZE` plus Windows `FD_CREATETIME` (0x08 mistyped as “unix mode”). Remote CliprdrStream trusted a bad/zero stream length and returned EOF without `FILECONTENTS_RANGE`. Descriptors now match RustDesk (`FD_ATTRIBUTES | FD_WRITESTIME | FD_PROGRESSUI`, size via `FILECONTENTS_SIZE` probe); FileContents rejects empty RANGE ACKs and serializes responses. Requires rebuilt `rdclient-desktop` **and** panel update (`cliprdr.js`). Verify: paste/upload a non-empty local file and confirm remote size matches.
diff --git a/betterdesk-server/signal/handler.go b/betterdesk-server/signal/handler.go
index 3c1afae7..71052514 100644
--- a/betterdesk-server/signal/handler.go
+++ b/betterdesk-server/signal/handler.go
@@ -1909,6 +1909,9 @@ func (s *Server) authorizeRelayTicket(relayUUID, initiatorID, targetID string) b
 //  2. Valid BetterDesk client login token on the punch/relay message (#327)
 //  3. Panel signal-proxy CIDR (Web Remote)
 //  4. Live peer with exact ip:port match (FindByAddr)
+//  5. Exactly one live peer at the same public IP (safe FindByIP fallback for
+//     stock clients that PunchHole on a new TCP port). Multiple live peers at
+//     that IP → initiator_ambiguous_same_nat (no identity inheritance, #302)
 //
 // Managed and locked modes additionally require an approved DB peer row (pending
 // enrollment alone is not enough). Panel proxy initiators skip peer-map / DB
@@ -1948,10 +1951,25 @@ func (s *Server) requireAuthorizedInitiator(raddr *net.UDPAddr, targetID, token
 		return s.finalizeAuthorizedInitiator(initiator.ID, raddr, targetID, initiator.Banned)
 	}
 
-	// Never inherit an identity solely from a public IP address. NAT addresses
-	// are shared and attacker-controlled source ports are trivial to create.
-	s.logUnauthorizedInitiator(raddr, "", targetID, "initiator_not_registered")
-	return "", false
+	// 5. Safe IP-only fallback: stock RustDesk opens PunchHole on a new TCP
+	// port after RegisterPk/UDP heartbeat, so FindByAddr misses. Authorize only
+	// when exactly one live peer shares this public IP.
+	var live []*peer.Entry
+	for _, e := range s.peers.FindAllByIP(raddr.IP) {
+		if e != nil && !e.IsExpired(config.RegTimeout) {
+			live = append(live, e)
+		}
+	}
+	switch len(live) {
+	case 0:
+		s.logUnauthorizedInitiator(raddr, "", targetID, "initiator_not_registered")
+		return "", false
+	case 1:
+		return s.finalizeAuthorizedInitiator(live[0].ID, raddr, targetID, live[0].Banned)
+	default:
+		s.logUnauthorizedInitiator(raddr, "", targetID, "initiator_ambiguous_same_nat")
+		return "", false
+	}
 }
 
 // bindTCPSessionPeer records the peer ID on an open tcpPunchConn so a later
diff --git a/betterdesk-server/signal/handler_test.go b/betterdesk-server/signal/handler_test.go
index 0a25fafe..41170d4e 100644
--- a/betterdesk-server/signal/handler_test.go
+++ b/betterdesk-server/signal/handler_test.go
@@ -1246,16 +1246,16 @@ func TestExactAddrInitiatorAuthorized(t *testing.T) {
 		t.Fatalf("exact addr auth = (%q, %v), want EXACTINIT1", id, ok)
 	}
 
-	// A different port at the same public IP is not an authenticated identity.
+	// Sole live peer at this IP: stock clients PunchHole on a new TCP port.
 	id, ok = srv.requireAuthorizedInitiator(udpAddr("198.51.100.81", 51001), "TGTEXACT1", "")
-	if ok || id != "" {
-		t.Fatalf("IP-only fallback auth = (%q, %v), want rejection", id, ok)
+	if !ok || id != "EXACTINIT1" {
+		t.Fatalf("single-IP fallback auth = (%q, %v), want EXACTINIT1", id, ok)
 	}
 }
 
-func TestSingleIPFallbackRejectsDifferentPort(t *testing.T) {
-	// A stock client must use the same registered endpoint, a bound TCP
-	// session, or an opaque client token; a shared NAT address is insufficient.
+func TestSingleIPFallbackAuthorizesDifferentPort(t *testing.T) {
+	// Stock RustDesk PunchHole uses a new TCP port; with exactly one live peer
+	// at the public IP, authorize via FindAllByIP (3.5.15 / regression after 3.5.16).
 	srv, database := newTestSignalServer(t, config.EnrollmentModeOpen)
 	if err := database.UpsertPeer(&db.Peer{ID: "SOLEINIT1", Status: "ONLINE", IP: "78.31.94.73"}); err != nil {
 		t.Fatalf("UpsertPeer: %v", err)
@@ -1264,13 +1264,13 @@ func TestSingleIPFallbackRejectsDifferentPort(t *testing.T) {
 	putOnlinePeer(srv, "TGTSINGLE1", "203.0.113.90", 52000, peer.ConnTCP)
 
 	id, ok := srv.requireAuthorizedInitiator(udpAddr("78.31.94.73", 55041), "TGTSINGLE1", "")
-	if ok || id != "" {
-		t.Fatalf("IP-only fallback = (%q, %v), want rejection", id, ok)
+	if !ok || id != "SOLEINIT1" {
+		t.Fatalf("single-IP fallback = (%q, %v), want SOLEINIT1", id, ok)
 	}
 
 	resp := srv.handlePunchHoleRequestTCP(&pb.PunchHoleRequest{Id: "TGTSINGLE1"}, udpAddr("78.31.94.73", 55041))
-	if phr := resp.GetPunchHoleResponse(); phr == nil || phr.Failure != pb.PunchHoleResponse_ID_NOT_EXIST {
-		t.Fatalf("IP-only PunchHole must be unauthorized, got %+v", resp)
+	if phr := resp.GetPunchHoleResponse(); phr != nil && phr.Failure == pb.PunchHoleResponse_ID_NOT_EXIST {
+		t.Fatal("single live peer PunchHole must not be refused as unauthorized")
 	}
 }