diff --git a/chatmaild/src/chatmaild/metadata.py b/chatmaild/src/chatmaild/metadata.py
index 97fc9bc..74be624 100644
--- a/chatmaild/src/chatmaild/metadata.py
+++ b/chatmaild/src/chatmaild/metadata.py
@@ -34,10 +34,8 @@ class Metadata:
 
     def add_token_to_addr(self, addr, token):
         with self.get_metadata_dict(addr).modify() as data:
-            tokens = data.get(self.DEVICETOKEN_KEY)
-            if tokens is None:
-                data[self.DEVICETOKEN_KEY] = [token]
-            elif token not in tokens:
+            tokens = data.setdefault(self.DEVICETOKEN_KEY, [])
+            if token not in tokens:
                 tokens.append(token)
 
     def remove_token_from_addr(self, addr, token):
@@ -130,8 +128,7 @@ def main():
         return 1
 
     notification_dir = vmail_dir / "pending_notifications"
-    if not notification_dir.exists():
-        notification_dir.mkdir()
+    notification_dir.mkdir(exist_ok=True)
     metadata = Metadata(vmail_dir)
     notifier = Notifier(notification_dir)
     notifier.start_notification_threads(metadata.remove_token_from_addr)
diff --git a/chatmaild/src/chatmaild/notifier.py b/chatmaild/src/chatmaild/notifier.py
index 4de05fc..b23cbd3 100644
--- a/chatmaild/src/chatmaild/notifier.py
+++ b/chatmaild/src/chatmaild/notifier.py
@@ -1,16 +1,14 @@
 """
 This modules provides notification machinery for transmitting device tokens to
-a central notification server which in turns contacts a phone provider's notification server
+a central notification server which in turn contacts a phone provider's notification server
 to trigger Delta Chat apps to retrieve messages and provide instant notifications to users.
 
 The Notifier class arranges the queuing of tokens in separate PriorityQueues
 from which NotifyThreads take and transmit them via HTTPS
-to the `notifications.delta.chat` service
-which in turn contacts a phone's providers's notification service
-which in turn wakes up the Delta Chat app on user devices.
-The lack of proper HTTP2-support in Python lets us
-use multiple threads and connections to the Rust-implemented `notifications.delta.chat`
-which however uses HTTP2 and thus only a single connection to phone-notification providers.
+to the `notifications.delta.chat` service.
+The current lack of proper HTTP/2-support in Python leads us
+to use multiple threads and connections to the Rust-implemented `notifications.delta.chat`
+which itself uses HTTP/2 and thus only a single connection to phone-notification providers.
 
 If a token fails to cause a successful notification
 it is moved to a retry-number specific PriorityQueue
@@ -87,7 +85,7 @@ class Notifier:
 
         when = time.time()
         if retry_num > 0:
-            # backup exponentially with number of retries
+            # back off exponentially with number of retries
             when += pow(self.NOTIFICATION_RETRY_DELAY, retry_num)
         self.retry_queues[retry_num].put((when, queue_item))
 
@@ -96,7 +94,7 @@ class Notifier:
         threads = {}
         for retry_num in range(len(self.retry_queues)):
             # use 4 threads for first-try tokens and less for subsequent tries
-            num_threads = {0: 4}.get(retry_num, 2)
+            num_threads = 4 if retry_num == 0 else 2
             threads[retry_num] = []
             for _ in range(num_threads):
                 thread = NotifyThread(self, retry_num, remove_token_from_addr)