fixed last_sent_time global issue

app.py

@@ -679,11 +679,10 @@ def send_notifications_for_events(new_events):
         import time
 
         send_lock = threading.Lock()
-        last_sent_time = 0
+        last_sent_time = [0]
 
 
         def rate_limited_send(mail, subject, html):
-            global last_sent_time
 
             with send_lock:
                 now = time.time()