diff --git a/server/db/mysql/group_message_shards.go b/server/db/mysql/group_message_shards.go
index 13f8ca0..a472f3b 100644
--- a/server/db/mysql/group_message_shards.go
+++ b/server/db/mysql/group_message_shards.go
@@ -138,6 +138,17 @@ func groupMessageTablesForSeq(q sqlx.QueryerContext, ctx context.Context, tenant
 			return nil, err
 		}
 	}
+	tables := groupMessageShardTablesForSeq(tenantID, routes, seq)
+	if len(tables) == 0 && cached {
+		if routes, err = groupMessageAllShardRoutes(q, ctx, tenantID); err != nil {
+			return nil, err
+		}
+		tables = groupMessageShardTablesForSeq(tenantID, routes, seq)
+	}
+	return tables, nil
+}
+
+func groupMessageShardTablesForSeq(tenantID t.TenantID, routes []store.GroupMessageShardRoute, seq int64) []string {
 	tables := make([]string, 0, 2)
 	for _, route := range routes {
 		if route.MinSeq <= seq && route.MaxSeq >= seq {
@@ -146,7 +157,7 @@ func groupMessageTablesForSeq(q sqlx.QueryerContext, ctx context.Context, tenant
 			}
 		}
 	}
-	return tables, nil
+	return tables
 }
 
 func groupMessageAllShardRoutes(q sqlx.QueryerContext, ctx context.Context, tenantID t.TenantID) ([]store.GroupMessageShardRoute, error) {
diff --git a/server/db/mysql/group_schema_test.go b/server/db/mysql/group_schema_test.go
index 01b324a..76f6dca 100644
--- a/server/db/mysql/group_schema_test.go
+++ b/server/db/mysql/group_schema_test.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/tinode/chat/server/store"
 	types "github.com/tinode/chat/server/store/types"
 )
 
@@ -75,6 +76,21 @@ func TestGroupMessageShardTableRejectsUnsafeMonth(t *testing.T) {
 	}
 }
 
+func TestGroupMessageShardTablesForSeqFiltersRoutes(t *testing.T) {
+	routes := []store.GroupMessageShardRoute{
+		{Month: "202608", MinSeq: 1, MaxSeq: 20},
+		{Month: "202609", MinSeq: 21, MaxSeq: 100},
+		{Month: "202613", MinSeq: 1, MaxSeq: 1000},
+	}
+	tables := groupMessageShardTablesForSeq(7, routes, 23)
+	if len(tables) != 1 || tables[0] != "im_007_group_messages_202609" {
+		t.Fatalf("unexpected shard tables for seq: %#v", tables)
+	}
+	if tables = groupMessageShardTablesForSeq(7, routes, 101); len(tables) != 0 {
+		t.Fatalf("unexpected shard tables for uncovered seq: %#v", tables)
+	}
+}
+
 func TestTenantPartitionTableNames(t *testing.T) {
 	tests := []struct {
 		tenantID types.TenantID
diff --git a/server/hub.go b/server/hub.go
index f1aa441..f18615c 100644
--- a/server/hub.go
+++ b/server/hub.go
@@ -255,14 +255,17 @@ func (h *Hub) run() {
 				}
 			} else if msg.Note == nil {
 				// Topic is unknown or offline.
-				// Note is silently ignored, all other messages are reported as accepted to prevent
-				// clients from guessing valid topic names.
+				// Note is silently ignored. Other client messages cannot be accepted here
+				// because they are not routed to a live topic and therefore cannot reserve a
+				// message seq or be persisted.
 
 				// TODO(gene): validate topic name, discarding invalid topics.
 
 				logs.Info.Printf("Hub. Topic[%s] is unknown or offline", msg.RcptTo)
 
-				msg.sess.queueOut(NoErrAcceptedExplicitTs(msg.Id, msg.RcptTo, types.TimeNow(), msg.Timestamp))
+				if msg.sess != nil {
+					msg.sess.queueOut(ErrAttachFirst(msg, types.TimeNow()))
+				}
 			}
 		case msg := <-h.routeSrv:
 			// This is a server message from a connection not subscribed to topic
diff --git a/server/hub_tenant_test.go b/server/hub_tenant_test.go
index df23e7b..01c38aa 100644
--- a/server/hub_tenant_test.go
+++ b/server/hub_tenant_test.go
@@ -1,8 +1,10 @@
 package main
 
 import (
+	"net/http"
 	"sync"
 	"testing"
+	"time"
 
 	"github.com/tinode/chat/server/store/types"
 )
@@ -53,3 +55,50 @@ func TestTopicAssignsTenantToServerMessage(t *testing.T) {
 		t.Fatalf("message tenant = %d, want %d", msg.TenantID, topic.tenantID)
 	}
 }
+
+func TestHubRejectsUnroutedClientMessageInsteadOfAcceptingWithoutSeq(t *testing.T) {
+	h := &Hub{
+		topics:     &sync.Map{},
+		routeCli:   make(chan *ClientComMessage, 1),
+		shutdown:   make(chan chan<- bool),
+		routeSrv:   make(chan *ServerComMessage),
+		join:       make(chan *ClientComMessage),
+		meta:       make(chan *ClientComMessage),
+		unreg:      make(chan *topicUnreg),
+		userStatus: make(chan *userStatusReq),
+		rehash:     make(chan bool),
+	}
+	go h.run()
+	done := make(chan bool)
+	defer func() {
+		h.shutdown <- done
+		<-done
+	}()
+
+	sess := &Session{tenantID: 7, send: make(chan any, 1)}
+	now := time.Now().UTC()
+	h.routeCli <- &ClientComMessage{
+		Id:        "pub-1",
+		TenantID:  7,
+		RcptTo:    "p2pMissing",
+		Original:  "p2pMissing",
+		Timestamp: now,
+		sess:      sess,
+	}
+
+	select {
+	case raw := <-sess.send:
+		msg, ok := raw.(*ServerComMessage)
+		if !ok || msg.Ctrl == nil {
+			t.Fatalf("unexpected response: %#v", raw)
+		}
+		if msg.Ctrl.Code != http.StatusConflict || msg.Ctrl.Text != "must attach first" {
+			t.Fatalf("unexpected ctrl: %#v", msg.Ctrl)
+		}
+		if msg.Ctrl.Params != nil {
+			t.Fatalf("unrouted message must not expose seq params: %#v", msg.Ctrl.Params)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("timeout waiting for unrouted message response")
+	}
+}