Add config to change the delay before sending a notification email (#16696)

changelog.d/16696.feature

+Add a setting to be able to tweak the delay without interaction before an email is sent following a notification.

docs/usage/configuration/config_documentation.md

@@ -680,6 +680,11 @@ This setting has the following sub-options:
    has missed. Disabled by default.
 * `notif_for_new_users`: Set to false to disable automatic subscription to email
    notifications for new users. Enabled by default.
+* `notif_delay_before_mail`: The time to wait before emailing about a notification.
+  This gives the user a chance to view the message via push or an open client.
+  Defaults to 10 minutes.
+
+  _New in Synapse 1.99.0._
 * `client_base_url`: Custom URL for client links within the email notifications. By default
    links will be based on "https://matrix.to". (This setting used to be called `riot_base_url`;
    the old name is still supported for backwards-compatibility but is now deprecated.)

synapse/config/emailconfig.py

@@ -294,6 +294,11 @@ class EmailConfig(Config):
             self.email_riot_base_url = email_config.get(
                 "client_base_url", email_config.get("riot_base_url", None)
             )
+            # The amount of time we always wait before ever emailing about a notification
+            # (to give the user a chance to respond to other push or notice the window)
+            self.notif_delay_before_mail_ms = Config.parse_duration(
+                email_config.get("notif_delay_before_mail", "10m")
+            )
 
         if self.root.account_validity.account_validity_renew_by_email_enabled:
             expiry_template_html = email_config.get(

synapse/push/emailpusher.py

@@ -30,14 +30,9 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
-# The amount of time we always wait before ever emailing about a notification
-# (to give the user a chance to respond to other push or notice the window)
-DELAY_BEFORE_MAIL_MS = 10 * 60 * 1000
-
 # THROTTLE is the minimum time between mail notifications sent for a given room.
 # Each room maintains its own throttle counter, but each new mail notification
 # sends the pending notifications for all rooms.
-THROTTLE_START_MS = 10 * 60 * 1000
 THROTTLE_MAX_MS = 24 * 60 * 60 * 1000  # 24h
 # THROTTLE_MULTIPLIER = 6              # 10 mins, 1 hour, 6 hours, 24 hours
 THROTTLE_MULTIPLIER = 144  # 10 mins, 24 hours - i.e. jump straight to 1 day
@@ -80,6 +75,8 @@ class EmailPusher(Pusher):
         except ValueError:
             raise PusherConfigException("Invalid email")
 
+        self._delay_before_mail_ms = self.hs.config.email.notif_delay_before_mail_ms
+
     def on_started(self, should_check_for_notifs: bool) -> None:
         """Called when this pusher has been started.
 
@@ -180,7 +177,7 @@ class EmailPusher(Pusher):
             received_at = push_action.received_ts
             if received_at is None:
                 received_at = 0
-            notif_ready_at = received_at + DELAY_BEFORE_MAIL_MS
+            notif_ready_at = received_at + self._delay_before_mail_ms
 
             room_ready_at = self.room_ready_to_notify_at(push_action.room_id)
 
@@ -196,7 +193,7 @@ class EmailPusher(Pusher):
                     "room_id": push_action.room_id,
                     "now": self.clock.time_msec(),
                     "received_at": received_at,
-                    "delay_before_mail_ms": DELAY_BEFORE_MAIL_MS,
+                    "delay_before_mail_ms": self._delay_before_mail_ms,
                     "last_sent_ts": self.get_room_last_sent_ts(push_action.room_id),
                     "throttle_ms": self.get_room_throttle_ms(push_action.room_id),
                 }
@@ -300,10 +297,10 @@ class EmailPusher(Pusher):
         current_throttle_ms = self.get_room_throttle_ms(room_id)
 
         if gap > THROTTLE_RESET_AFTER_MS:
-            new_throttle_ms = THROTTLE_START_MS
+            new_throttle_ms = self._delay_before_mail_ms
         else:
             if current_throttle_ms == 0:
-                new_throttle_ms = THROTTLE_START_MS
+                new_throttle_ms = self._delay_before_mail_ms
             else:
                 new_throttle_ms = min(
                     current_throttle_ms * THROTTLE_MULTIPLIER, THROTTLE_MAX_MS