diff --git a/src/Plugin/Mail/NoteMail.php b/src/Plugin/Mail/NoteMail.php
index e4a045e..7fa79bb 100644
--- a/src/Plugin/Mail/NoteMail.php
+++ b/src/Plugin/Mail/NoteMail.php
@@ -24,4 +24,19 @@ class NoteMail extends PhpMail {
     return $message;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function mail(array $message) {
+    // We're running inside a functional test.
+    if (\Drupal::config('system.mail')->get('interface.default') === 'test_mail_collector') {
+      $captured_emails = \Drupal::state()->get('system.test_mail_collector') ?: [];
+      $captured_emails[] = $message;
+      \Drupal::state()->set('system.test_mail_collector', $captured_emails);
+      return TRUE;
+    }
+
+    return parent::mail($message);
+  }
+
 }