diff --git a/notifier/database/drivers/base.py b/notifier/database/drivers/base.py
index 2a56c67..8b42ef4 100644
--- a/notifier/database/drivers/base.py
+++ b/notifier/database/drivers/base.py
@@ -93,7 +93,9 @@ def count_user_configs(self) -> int:
         """Count the number of subscribed users."""
 
     @abstractmethod
-    def get_notifiable_users(self, frequency: str) -> List[str]:
+    def get_notifiable_users(
+        self, frequency: str, post_lower_timestamp_limit: int
+    ) -> List[str]:
         """Get the list of IDs for users subscribed to the given channel
         frequency who have at least one notification waiting for them.
         """
diff --git a/notifier/database/drivers/mysql.py b/notifier/database/drivers/mysql.py
index 8d71532..1d0c413 100644
--- a/notifier/database/drivers/mysql.py
+++ b/notifier/database/drivers/mysql.py
@@ -332,9 +332,14 @@ def count_user_configs(self) -> int:
             )["count"],
         )
 
-    def get_notifiable_users(self, frequency: str) -> List[str]:
+    def get_notifiable_users(
+        self, frequency: str, post_lower_timestamp_limit: int
+    ) -> List[str]:
         logger.debug("Caching post context...")
-        self.execute_named("cache_post_context")
+        self.execute_named(
+            "cache_post_context",
+            {"post_lower_timestamp_limit": post_lower_timestamp_limit},
+        )
         logger.debug("Retrieving notifiable users users...")
         user_ids = [
             cast(str, row["user_id"])
diff --git a/notifier/database/queries/cache_post_context.sql b/notifier/database/queries/cache_post_context.sql
index aaa1ea7..e5abd9e 100644
--- a/notifier/database/queries/cache_post_context.sql
+++ b/notifier/database/queries/cache_post_context.sql
@@ -20,5 +20,8 @@ WITH cte AS (
   WHERE
     -- Remove deleted threads/posts
     thread.is_deleted = 0 AND post.is_deleted = 0
+
+    -- Remove posts from before the notification service started
+    AND post.posted_timestamp > %(post_lower_timestamp_limit)s
 )
 SELECT * FROM cte
\ No newline at end of file
diff --git a/notifier/notify.py b/notifier/notify.py
index 155d44b..58902f2 100644
--- a/notifier/notify.py
+++ b/notifier/notify.py
@@ -241,7 +241,7 @@ def notify_channel(
     # Filter the users only to those with notifications waiting
     logger.debug("Filtering users without notifications waiting...")
     user_count_pre_filter = len(user_configs)
-    notifiable_user_ids = database.get_notifiable_users(channel)
+    notifiable_user_ids = database.get_notifiable_users(channel, config["service_start_timestamp"])
     user_configs = [
         user for user in user_configs if user["user_id"] in notifiable_user_ids
     ]
diff --git a/tests/test_database.py b/tests/test_database.py
index 6d27bac..df7a3a3 100644
--- a/tests/test_database.py
+++ b/tests/test_database.py
@@ -456,7 +456,7 @@ def check_timestamp(n: int) -> None:
 
 
 @pytest.mark.needs_database
-def test_get_notifiable_users(sample_database: BaseDatabaseDriver) -> None:
+def test_get_notifiable_users(sample_database: MySqlDriver) -> None:
     """Test that the notifiable users list returns the correct set of users.
 
     The notifiable users utility lists directly from the database the set of
@@ -627,15 +627,18 @@ def test_get_notifiable_users(sample_database: BaseDatabaseDriver) -> None:
     for post in sample_posts:
         sample_database.store_post(post)
 
-    users_expected_to_have_notifications = {
+    assert set(sample_database.get_notifiable_users("hourly", 0)) == {
         "1",  # UserR1 from base sample DB
         "51",  # T5U-!P-Sub
         "53",  # T5U-Starter
         "55",  # T5U-Poster
     }
 
-    users_with_notifications = sample_database.get_notifiable_users("hourly")
+    with sample_database.transaction() as cursor:
+        cursor.execute("DROP TABLE post_with_context")
 
-    assert (
-        set(users_with_notifications) == users_expected_to_have_notifications
-    )
+    assert set(sample_database.get_notifiable_users("hourly", 99)) == {
+        "51",  # T5U-!P-Sub
+        "53",  # T5U-Starter
+        "55",  # T5U-Poster
+    }