diff --git a/api/hook_test.go b/api/hook_test.go
index 1362647a..4f952bb1 100644
--- a/api/hook_test.go
+++ b/api/hook_test.go
@@ -114,10 +114,11 @@ func TestHookRetry(t *testing.T) {
 	svr := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		callCount++
 		assert.EqualValues(t, 0, r.ContentLength)
+		// 503 is retriable; eventual 200 succeeds on the third attempt.
 		if callCount == 3 {
 			w.WriteHeader(http.StatusOK)
 		} else {
-			w.WriteHeader(http.StatusBadRequest)
+			w.WriteHeader(http.StatusServiceUnavailable)
 		}
 	}))
 	defer svr.Close()
@@ -143,6 +144,66 @@ func TestHookRetry(t *testing.T) {
 	assert.Equal(t, 3, callCount)
 }
 
+func TestHookNonRetriable4xxDoesNotRetry(t *testing.T) {
+	var callCount int
+	svr := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		callCount++
+		w.WriteHeader(http.StatusBadRequest)
+	}))
+	defer svr.Close()
+	localhost := removeLocalhostFromPrivateIPBlock()
+	defer unshiftPrivateIPBlock(localhost)
+
+	config := &conf.WebhookConfig{
+		URL:     svr.URL,
+		Retries: 3,
+	}
+	w := Webhook{
+		WebhookConfig: config,
+	}
+	_, err := w.trigger()
+	require.Error(t, err)
+
+	herr, ok := err.(*HTTPError)
+	require.True(t, ok, "expected an *HTTPError, got %T", err)
+	assert.Equal(t, http.StatusBadRequest, herr.Code)
+
+	// 4xx (other than 401, which is the deny path) must not retry.
+	assert.Equal(t, 1, callCount)
+}
+
+func TestHookRetries429(t *testing.T) {
+	var callCount int
+	svr := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		callCount++
+		if callCount == 3 {
+			w.WriteHeader(http.StatusOK)
+		} else {
+			w.WriteHeader(http.StatusTooManyRequests)
+		}
+	}))
+	defer svr.Close()
+	localhost := removeLocalhostFromPrivateIPBlock()
+	defer unshiftPrivateIPBlock(localhost)
+
+	config := &conf.WebhookConfig{
+		URL:     svr.URL,
+		Retries: 3,
+	}
+	w := Webhook{
+		WebhookConfig: config,
+	}
+	b, err := w.trigger()
+	defer func() {
+		if b != nil {
+			b.Close()
+		}
+	}()
+	require.NoError(t, err)
+
+	assert.Equal(t, 3, callCount)
+}
+
 func TestHookTimeout(t *testing.T) {
 	var callCount int
 	svr := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
diff --git a/api/hooks.go b/api/hooks.go
index 80242246..751e39ca 100644
--- a/api/hooks.go
+++ b/api/hooks.go
@@ -80,6 +80,9 @@ func (w *Webhook) trigger() (io.ReadCloser, error) {
 	client.Transport = SafeRoundtripper(client.Transport, hooklog)
 
 	for i := 0; i < w.Retries; i++ {
+		if i > 0 {
+			time.Sleep(backoffDelay(i))
+		}
 		hooklog = hooklog.WithField("attempt", i+1)
 		hooklog.Info("Starting to perform signup hook request")
 
@@ -134,9 +137,17 @@ func (w *Webhook) trigger() (io.ReadCloser, error) {
 				body = rsp.Body
 			}
 			return body, nil
-		default:
-			rspLog.Infof("Bad response for webhook %d in %s", rsp.StatusCode, dur)
 		}
+
+		if rsp.StatusCode == http.StatusTooManyRequests || rsp.StatusCode >= 500 {
+			rspLog.Infof("Retriable response from webhook %d in %s", rsp.StatusCode, dur)
+			closeBody(rsp)
+			continue
+		}
+
+		rspLog.Infof("Non-retriable response from webhook %d in %s", rsp.StatusCode, dur)
+		closeBody(rsp)
+		return nil, httpError(rsp.StatusCode, "Webhook returned status %d", rsp.StatusCode)
 	}
 
 	hooklog.Infof("Failed to process webhook for %s after %d attempts", w.URL, w.Retries)
@@ -314,3 +325,13 @@ type connectionWatcher struct {
 func (c *connectionWatcher) GotConn(_ httptrace.GotConnInfo) {
 	c.gotConn = true
 }
+
+func backoffDelay(attempt int) time.Duration {
+	const base = 100 * time.Millisecond
+	const max = 2 * time.Second
+	delay := base * time.Duration(1<<(attempt-1))
+	if delay > max {
+		delay = max
+	}
+	return delay
+}