diff --git a/appservice/consumers/roomserver.go b/appservice/consumers/roomserver.go
index 06b3c5a69..cde02348d 100644
--- a/appservice/consumers/roomserver.go
+++ b/appservice/consumers/roomserver.go
@@ -74,10 +74,12 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 	if err := json.Unmarshal(msg.Data, &output); err != nil {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("roomserver output log: message parse failure")
+		_ = msg.Nak()
 		return
 	}
 
 	if output.Type != api.OutputTypeNewRoomEvent {
+		_ = msg.Nak()
 		return
 	}
 
@@ -87,7 +89,11 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 	// Send event to any relevant application services
 	if err := s.filterRoomserverEvents(context.TODO(), events); err != nil {
 		log.WithError(err).Errorf("roomserver output log: filter error")
+		_ = msg.Nak()
+		return
 	}
+
+	_ = msg.Ack()
 }
 
 // filterRoomserverEvents takes in events and decides whether any of them need
diff --git a/federationsender/consumers/eduserver.go b/federationsender/consumers/eduserver.go
index c29226eb9..5fee5b48f 100644
--- a/federationsender/consumers/eduserver.go
+++ b/federationsender/consumers/eduserver.go
@@ -81,6 +81,7 @@ func (t *OutputEDUConsumer) onSendToDeviceEvent(msg *nats.Msg) {
 	var ote api.OutputSendToDeviceEvent
 	if err := json.Unmarshal(msg.Data, &ote); err != nil {
 		log.WithError(err).Errorf("eduserver output log: message parse failed (expected send-to-device)")
+		_ = msg.Nak()
 		return
 	}
 
@@ -88,16 +89,19 @@ func (t *OutputEDUConsumer) onSendToDeviceEvent(msg *nats.Msg) {
 	_, originServerName, err := gomatrixserverlib.SplitID('@', ote.Sender)
 	if err != nil {
 		log.WithError(err).WithField("user_id", ote.Sender).Error("Failed to extract domain from send-to-device sender")
+		_ = msg.Nak()
 		return
 	}
 	if originServerName != t.ServerName {
 		log.WithField("other_server", originServerName).Info("Suppressing send-to-device: originated elsewhere")
+		_ = msg.Nak()
 		return
 	}
 
 	_, destServerName, err := gomatrixserverlib.SplitID('@', ote.UserID)
 	if err != nil {
 		log.WithError(err).WithField("user_id", ote.UserID).Error("Failed to extract domain from send-to-device destination")
+		_ = msg.Nak()
 		return
 	}
 
@@ -118,6 +122,7 @@ func (t *OutputEDUConsumer) onSendToDeviceEvent(msg *nats.Msg) {
 	}
 	if edu.Content, err = json.Marshal(tdm); err != nil {
 		log.WithError(err).Error("failed to marshal EDU JSON")
+		_ = msg.Nak()
 		return
 	}
 
@@ -125,6 +130,8 @@ func (t *OutputEDUConsumer) onSendToDeviceEvent(msg *nats.Msg) {
 	if err := t.queues.SendEDU(edu, t.ServerName, []gomatrixserverlib.ServerName{destServerName}); err != nil {
 		log.WithError(err).Error("failed to send EDU")
 	}
+
+	_ = msg.Ack()
 }
 
 // onTypingEvent is called in response to a message received on the typing
@@ -135,6 +142,7 @@ func (t *OutputEDUConsumer) onTypingEvent(msg *nats.Msg) {
 	if err := json.Unmarshal(msg.Data, &ote); err != nil {
 		// Skip this msg but continue processing messages.
 		log.WithError(err).Errorf("eduserver output log: message parse failed (expected typing)")
+		_ = msg.Nak()
 		return
 	}
 
@@ -142,6 +150,7 @@ func (t *OutputEDUConsumer) onTypingEvent(msg *nats.Msg) {
 	_, typingServerName, err := gomatrixserverlib.SplitID('@', ote.Event.UserID)
 	if err != nil {
 		log.WithError(err).WithField("user_id", ote.Event.UserID).Error("Failed to extract domain from typing sender")
+		_ = msg.Nak()
 		return
 	}
 	if typingServerName != t.ServerName {
@@ -166,12 +175,15 @@ func (t *OutputEDUConsumer) onTypingEvent(msg *nats.Msg) {
 		"typing":  ote.Event.Typing,
 	}); err != nil {
 		log.WithError(err).Error("failed to marshal EDU JSON")
+		_ = msg.Nak()
 		return
 	}
 
 	if err := t.queues.SendEDU(edu, t.ServerName, names); err != nil {
 		log.WithError(err).Error("failed to send EDU")
 	}
+
+	_ = msg.Ack()
 }
 
 // onReceiptEvent is called in response to a message received on the receipt
@@ -182,6 +194,7 @@ func (t *OutputEDUConsumer) onReceiptEvent(msg *nats.Msg) {
 	if err := json.Unmarshal(msg.Data, &receipt); err != nil {
 		// Skip this msg but continue processing messages.
 		log.WithError(err).Errorf("eduserver output log: message parse failed (expected receipt)")
+		_ = msg.Nak()
 		return
 	}
 
@@ -189,9 +202,11 @@ func (t *OutputEDUConsumer) onReceiptEvent(msg *nats.Msg) {
 	_, receiptServerName, err := gomatrixserverlib.SplitID('@', receipt.UserID)
 	if err != nil {
 		log.WithError(err).WithField("user_id", receipt.UserID).Error("failed to extract domain from receipt sender")
+		_ = msg.Nak()
 		return
 	}
 	if receiptServerName != t.ServerName {
+		_ = msg.Nak()
 		return // don't log, very spammy as it logs for each remote receipt
 	}
 
@@ -224,10 +239,13 @@ func (t *OutputEDUConsumer) onReceiptEvent(msg *nats.Msg) {
 	}
 	if edu.Content, err = json.Marshal(content); err != nil {
 		log.WithError(err).Error("failed to marshal EDU JSON")
+		_ = msg.Nak()
 		return
 	}
 
 	if err := t.queues.SendEDU(edu, t.ServerName, names); err != nil {
 		log.WithError(err).Error("failed to send EDU")
 	}
+
+	_ = msg.Ack()
 }
diff --git a/federationsender/consumers/roomserver.go b/federationsender/consumers/roomserver.go
index a4b776d83..61db7e84c 100644
--- a/federationsender/consumers/roomserver.go
+++ b/federationsender/consumers/roomserver.go
@@ -76,6 +76,7 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 	if err := json.Unmarshal(msg.Data, &output); err != nil {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("roomserver output log: message parse failure")
+		_ = msg.Nak()
 		return
 	}
 
@@ -96,6 +97,7 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 				log.WithField("error", output.Type).Info(
 					err.Error(),
 				)
+				_ = msg.Nak()
 			default:
 				// panic rather than continue with an inconsistent database
 				log.WithFields(log.Fields{
@@ -108,6 +110,9 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 			}
 			return
 		}
+
+		_ = msg.Ack()
+
 	case api.OutputTypeNewInboundPeek:
 		if err := s.processInboundPeek(*output.NewInboundPeek); err != nil {
 			log.WithFields(log.Fields{
@@ -116,10 +121,13 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 			}).Panicf("roomserver output log: remote peek event failure")
 			return
 		}
+		_ = msg.Ack()
+
 	default:
 		log.WithField("type", output.Type).Debug(
 			"roomserver output log: ignoring unknown output type",
 		)
+		_ = msg.Ack()
 		return
 	}
 }
diff --git a/syncapi/consumers/clientapi.go b/syncapi/consumers/clientapi.go
index b5ae32a00..9f80f0600 100644
--- a/syncapi/consumers/clientapi.go
+++ b/syncapi/consumers/clientapi.go
@@ -74,6 +74,7 @@ func (s *OutputClientDataConsumer) onMessage(msg *nats.Msg) {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("client API server output log: message parse failure")
 		sentry.CaptureException(err)
+		_ = msg.Nak()
 		return
 	}
 
@@ -96,4 +97,6 @@ func (s *OutputClientDataConsumer) onMessage(msg *nats.Msg) {
 
 	s.stream.Advance(streamPos)
 	s.notifier.OnNewAccountData(userID, types.StreamingToken{AccountDataPosition: streamPos})
+
+	_ = msg.Ack()
 }
diff --git a/syncapi/consumers/eduserver_receipts.go b/syncapi/consumers/eduserver_receipts.go
index f8aa7a5f6..7b3e984af 100644
--- a/syncapi/consumers/eduserver_receipts.go
+++ b/syncapi/consumers/eduserver_receipts.go
@@ -70,6 +70,7 @@ func (s *OutputReceiptEventConsumer) onMessage(msg *nats.Msg) {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("EDU server output log: message parse failure")
 		sentry.CaptureException(err)
+		_ = msg.Nak()
 		return
 	}
 
@@ -88,4 +89,6 @@ func (s *OutputReceiptEventConsumer) onMessage(msg *nats.Msg) {
 
 	s.stream.Advance(streamPos)
 	s.notifier.OnNewReceipt(output.RoomID, types.StreamingToken{ReceiptPosition: streamPos})
+
+	_ = msg.Ack()
 }
diff --git a/syncapi/consumers/eduserver_sendtodevice.go b/syncapi/consumers/eduserver_sendtodevice.go
index 54c13897d..d8c43a856 100644
--- a/syncapi/consumers/eduserver_sendtodevice.go
+++ b/syncapi/consumers/eduserver_sendtodevice.go
@@ -74,15 +74,18 @@ func (s *OutputSendToDeviceEventConsumer) onMessage(msg *nats.Msg) {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("EDU server output log: message parse failure")
 		sentry.CaptureException(err)
+		_ = msg.Nak()
 		return
 	}
 
 	_, domain, err := gomatrixserverlib.SplitID('@', output.UserID)
 	if err != nil {
 		sentry.CaptureException(err)
+		_ = msg.Nak()
 		return
 	}
 	if domain != s.serverName {
+		_ = msg.Nak()
 		return
 	}
 
@@ -108,4 +111,6 @@ func (s *OutputSendToDeviceEventConsumer) onMessage(msg *nats.Msg) {
 		[]string{output.DeviceID},
 		types.StreamingToken{SendToDevicePosition: streamPos},
 	)
+
+	_ = msg.Ack()
 }
diff --git a/syncapi/consumers/eduserver_typing.go b/syncapi/consumers/eduserver_typing.go
index f6f63050b..47c5da685 100644
--- a/syncapi/consumers/eduserver_typing.go
+++ b/syncapi/consumers/eduserver_typing.go
@@ -71,6 +71,7 @@ func (s *OutputTypingEventConsumer) onMessage(msg *nats.Msg) {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("EDU server output log: message parse failure")
 		sentry.CaptureException(err)
+		_ = msg.Nak()
 		return
 	}
 
@@ -94,4 +95,6 @@ func (s *OutputTypingEventConsumer) onMessage(msg *nats.Msg) {
 
 	s.stream.Advance(typingPos)
 	s.notifier.OnNewTyping(output.Event.RoomID, types.StreamingToken{TypingPosition: typingPos})
+
+	_ = msg.Ack()
 }
diff --git a/syncapi/consumers/roomserver.go b/syncapi/consumers/roomserver.go
index fbe4408f4..c6e1c23a7 100644
--- a/syncapi/consumers/roomserver.go
+++ b/syncapi/consumers/roomserver.go
@@ -83,6 +83,7 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 	if err = json.Unmarshal(msg.Data, &output); err != nil {
 		// If the message was invalid, log it and move on to the next message in the stream
 		log.WithError(err).Errorf("roomserver output log: message parse failure")
+		_ = msg.Nak()
 		return
 	}
 
@@ -115,10 +116,15 @@ func (s *OutputRoomEventConsumer) onMessage(msg *nats.Msg) {
 		log.WithField("type", output.Type).Debug(
 			"roomserver output log: ignoring unknown output type",
 		)
+		_ = msg.Nak()
 	}
 	if err != nil {
 		log.WithError(err).Error("roomserver output log: failed to process event")
+		_ = msg.Nak()
+		return
 	}
+
+	_ = msg.Ack()
 }
 
 func (s *OutputRoomEventConsumer) onRedactEvent(