diff --git a/pkg/channels/base.go b/pkg/channels/base.go
index bd4ced849..b51eadb6e 100644
--- a/pkg/channels/base.go
+++ b/pkg/channels/base.go
@@ -18,6 +18,9 @@ import (
 	"github.com/sipeed/picoclaw/pkg/media"
 )
 
+// ForbiddenReplyText is the message sent to unauthorized users who message the bot.
+const ForbiddenReplyText = "You are not authorized to use this bot."
+
 var (
 	uniqueIDCounter uint64
 	uniqueIDPrefix  string
@@ -259,10 +262,22 @@ func (c *BaseChannel) HandleMessage(
 	}
 	if sender.CanonicalID != "" || sender.PlatformID != "" {
 		if !c.IsAllowedSender(sender) {
+			logger.DebugCF(c.name, "Message blocked (not in allowlist)", map[string]any{"sender": sender.CanonicalID})
+			if c.owner != nil {
+				_, _ = c.owner.Send(ctx, bus.OutboundMessage{
+					Channel: c.name, ChatID: chatID, Content: ForbiddenReplyText,
+				})
+			}
 			return
 		}
 	} else {
 		if !c.IsAllowed(senderID) {
+			logger.DebugCF(c.name, "Message blocked (not in allowlist)", map[string]any{"sender_id": senderID})
+			if c.owner != nil {
+				_, _ = c.owner.Send(ctx, bus.OutboundMessage{
+					Channel: c.name, ChatID: chatID, Content: ForbiddenReplyText,
+				})
+			}
 			return
 		}
 	}
diff --git a/pkg/channels/base_test.go b/pkg/channels/base_test.go
index 6132b8bf9..421ef9c4b 100644
--- a/pkg/channels/base_test.go
+++ b/pkg/channels/base_test.go
@@ -1,12 +1,17 @@
 package channels
 
 import (
+	"context"
 	"testing"
 
 	"github.com/sipeed/picoclaw/pkg/bus"
 	"github.com/sipeed/picoclaw/pkg/config"
 )
 
+func newTestBus() *bus.MessageBus {
+	return bus.NewMessageBus()
+}
+
 func TestBaseChannelIsAllowed(t *testing.T) {
 	tests := []struct {
 		name      string
@@ -263,3 +268,65 @@ func TestIsAllowedSender(t *testing.T) {
 		})
 	}
 }
+
+func TestHandleMessageForbiddenReply(t *testing.T) {
+	const allowedID = "allowed:123"
+	const chatID = "chat-456"
+
+	tests := []struct {
+		name        string
+		sender      bus.SenderInfo
+		wantReplied bool
+	}{
+		{
+			name: "unauthorized sender receives forbidden reply",
+			sender: bus.SenderInfo{
+				Platform:    "test",
+				PlatformID:  "999",
+				CanonicalID: "test:999",
+			},
+			wantReplied: true,
+		},
+		{
+			name: "authorized sender does not receive forbidden reply",
+			sender: bus.SenderInfo{
+				Platform:    "test",
+				PlatformID:  "123",
+				CanonicalID: allowedID,
+			},
+			wantReplied: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mock := &mockChannel{}
+			mock.BaseChannel = *NewBaseChannel("test", nil, newTestBus(), []string{allowedID})
+			mock.SetOwner(mock)
+
+			mock.HandleMessage(
+				context.Background(),
+				bus.Peer{Kind: "direct", ID: chatID},
+				"msg-1", tt.sender.PlatformID, chatID, "hello",
+				nil, nil,
+				tt.sender,
+			)
+
+			if tt.wantReplied {
+				if len(mock.sentMessages) != 1 {
+					t.Fatalf("expected 1 forbidden reply, got %d", len(mock.sentMessages))
+				}
+				if mock.sentMessages[0].Content != ForbiddenReplyText {
+					t.Errorf("reply content = %q, want %q", mock.sentMessages[0].Content, ForbiddenReplyText)
+				}
+				if mock.sentMessages[0].ChatID != chatID {
+					t.Errorf("reply chatID = %q, want %q", mock.sentMessages[0].ChatID, chatID)
+				}
+			} else {
+				if len(mock.sentMessages) != 0 {
+					t.Fatalf("expected no reply for authorized sender, got %d", len(mock.sentMessages))
+				}
+			}
+		})
+	}
+}
diff --git a/pkg/channels/telegram/telegram.go b/pkg/channels/telegram/telegram.go
index 2d59de4dc..52ef82562 100644
--- a/pkg/channels/telegram/telegram.go
+++ b/pkg/channels/telegram/telegram.go
@@ -592,21 +592,25 @@ func (c *TelegramChannel) handleMessage(ctx context.Context, message *telego.Mes
 		DisplayName: user.FirstName,
 	}
 
+	chatID := message.Chat.ID
+	chatIDStr := fmt.Sprintf("%d", chatID)
+
 	// check allowlist to avoid downloading attachments for rejected users
 	if !c.IsAllowedSender(sender) {
 		logger.DebugCF("telegram", "Message rejected by allowlist", map[string]any{
 			"user_id": platformID,
 		})
+		_, _ = c.Send(ctx, bus.OutboundMessage{
+			Channel: "telegram", ChatID: chatIDStr, Content: channels.ForbiddenReplyText,
+		})
 		return nil
 	}
 
-	chatID := message.Chat.ID
 	c.chatIDs[platformID] = chatID
 
 	content := ""
 	mediaPaths := []string{}
 
-	chatIDStr := fmt.Sprintf("%d", chatID)
 	messageIDStr := fmt.Sprintf("%d", message.MessageID)
 	scope := channels.BuildMediaScope("telegram", chatIDStr, messageIDStr)
 
diff --git a/pkg/channels/whatsapp_native/whatsapp_native.go b/pkg/channels/whatsapp_native/whatsapp_native.go
index d0a74a405..38daca1a6 100644
--- a/pkg/channels/whatsapp_native/whatsapp_native.go
+++ b/pkg/channels/whatsapp_native/whatsapp_native.go
@@ -385,6 +385,8 @@ func (c *WhatsAppNativeChannel) handleIncoming(evt *events.Message) {
 	}
 
 	if !c.IsAllowedSender(sender) {
+		logger.DebugCF("whatsapp", "WhatsApp message blocked (not in allowlist)", map[string]any{"sender_id": senderID})
+		_, _ = c.Send(c.runCtx, bus.OutboundMessage{Channel: "whatsapp", ChatID: chatID, Content: channels.ForbiddenReplyText})
 		return
 	}