diff --git a/manager/dispatch.go b/manager/dispatch.go
index 0054e34a..f49dbbec 100644
--- a/manager/dispatch.go
+++ b/manager/dispatch.go
@@ -36,22 +36,17 @@ func (d *Dispatcher) notify(name string, alerts ...*Alert) {
 
 func (d *Dispatcher) Run() {
 	for {
-		log.Infoln("waiting")
 		alert := d.state.Alert().Next()
 
-		log.Infoln("received:", alert)
-
 		conf, err := d.state.Config().Get()
 		if err != nil {
 			log.Error(err)
 			continue
 		}
-		log.Infoln("retrieved config")
 
 		for _, m := range conf.Routes.Match(alert.Labels) {
 			d.processAlert(alert, m)
 		}
-		log.Infoln("processing done")
 	}
 }
 
@@ -68,20 +63,16 @@ func (d *Dispatcher) processAlert(alert *Alert, opts *RouteOpts) {
 
 	ag, ok := d.aggrGroups[fp]
 	if !ok {
-		ag = &aggrGroup{
-			dispatcher: d,
-
-			labels:    group,
-			wait:      opts.GroupWait(),
-			waitTimer: time.NewTimer(time.Hour),
-			notify:    opts.SendTo,
-		}
+		ag = newAggrGroup(group, opts)
 		d.aggrGroups[fp] = ag
-
-		go ag.run()
 	}
 
 	ag.insert(alert)
+
+	if ag.empty() {
+		ag.stop()
+		delete(d.aggrGroups, fp)
+	}
 }
 
 // aggrGroup aggregates alerts into groups based on
@@ -101,18 +92,31 @@ type aggrGroup struct {
 	mtx  sync.RWMutex
 }
 
-func (ag *aggrGroup) run() {
+// newAggrGroup returns a new aggregation group and starts background processing
+// that sends notifications about the contained alerts.
+func newAggrGroup(labels model.LabelSet, opts *RouteOpts) *aggrGroup {
+	ag := &aggrGroup{
+		dispatcher: d,
 
-	ag.waitTimer.Stop()
-
-	if ag.wait > 0 {
-		ag.waitTimer.Reset(ag.wait)
+		labels:    group,
+		wait:      opts.GroupWait(),
+		waitTimer: time.NewTimer(opts.GroupWait()),
+		notify:    opts.SendTo,
+		done:      make(chan bool),
+	}
+	if ag.wait == 0 {
+		ag.waitTimer.Stop()
 	}
 
+	go ag.run()
+
+	return ag
+}
+
+func (ag *aggrGroup) run() {
 	for {
 		select {
 		case <-ag.waitTimer.C:
-			log.Infoln("timer flush")
 			ag.flush()
 		case <-ag.done:
 			return
@@ -129,12 +133,18 @@ func (ag *aggrGroup) fingerprint() model.Fingerprint {
 	return ag.labels.Fingerprint()
 }
 
+// insert the alert into the aggregation group. If the aggregation group
+// is empty afterwards, true is returned.
 func (ag *aggrGroup) insert(alert *Alert) {
-	log.Infoln("insert:", alert)
+	ag.mtx.Lock()
 
 	ag.alertsNew = append(ag.alertsNew, alert)
 	sort.Sort(ag.alertsNew)
 
+	ag.mtx.Unlock()
+
+	// Immediately trigger a flush if the wait duration for this
+	// alert is already over.
 	if alert.Timestamp.Add(ag.wait).Before(time.Now()) {
 		ag.flush()
 	}
@@ -144,9 +154,15 @@ func (ag *aggrGroup) insert(alert *Alert) {
 	}
 }
 
-func (ag *aggrGroup) flush() {
-	log.Infoln("flush")
+func (ag *aggrGroup) empty() bool {
+	ag.mtx.RLock()
+	defer ag.mtx.RUnlock()
 
+	return len(ag.alertsNew)+len(ag.alertsOld) == 0
+}
+
+// flush sends notifications for all new alerts.
+func (ag *aggrGroup) flush() {
 	ag.mtx.Lock()
 	defer ag.mtx.Unlock()
 
@@ -156,16 +172,9 @@ func (ag *aggrGroup) flush() {
 	ag.alertsNew = ag.alertsNew[:0]
 }
 
+// alertTimeline is a list of alerts sorted by their timestamp.
 type alertTimeline []*Alert
 
-func (at alertTimeline) Len() int {
-	return len(at)
-}
-
-func (at alertTimeline) Less(i, j int) bool {
-	return at[i].Timestamp.Before(at[j].Timestamp)
-}
-
-func (at alertTimeline) Swap(i, j int) {
-	at[i], at[j] = at[j], at[i]
-}
+func (at alertTimeline) Len() int           { return len(at) }
+func (at alertTimeline) Less(i, j int) bool { return at[i].Timestamp.Before(at[j].Timestamp) }
+func (at alertTimeline) Swap(i, j int)      { at[i], at[j] = at[j], at[i] }