diff --git a/res/templates/mail.css b/res/templates/mail.css
index b02f509e5824..f2b5e84abc87 100644
--- a/res/templates/mail.css
+++ b/res/templates/mail.css
@@ -2,6 +2,11 @@ body {
     margin: 0px;
 }
 
+pre, code {
+    word-break: break-word;
+    white-space: pre-wrap;
+}
+
 #page {
     font-family: 'Open Sans', Helvetica, Arial, Sans-Serif;
     font-color: #454545;
diff --git a/res/templates/notif_mail.html b/res/templates/notif_mail.html
index 42560fdfd51b..dc13398df1bd 100644
--- a/res/templates/notif_mail.html
+++ b/res/templates/notif_mail.html
@@ -30,6 +30,17 @@
                         {% include 'room.html' with context %}
                     {% endfor %}
                     <div class="footer">
+                        <small>
+                            Sending email at {{ reason.now|format_ts("%c") }} due to activity in room '{{ reason.room_name }}' because:<br/>
+                            1. An event was received at {{ reason.received_at|format_ts("%c") }}
+                            which is more than {{ "%.1f"|format(reason.delay_before_mail_ms / (60*1000)) }} (delay_before_mail_ms) mins ago.<br/>
+                            {% if reason.last_sent_ts %}
+                                2. The last time we sent a mail for this room was {{ reason.last_sent_ts|format_ts("%c") }},
+                                which is more than {{ "%.1f"|format(reason.throttle_ms / (60*1000)) }} (current throttle_ms) mins ago.
+                            {% else %}
+                                2. We can't remember the last time we sent a mail for this room.
+                            {% endif %}
+                        </small>
                         <a href="{{ unsubscribe_link }}">Unsubscribe</a>
                     </div>
                 </td>
diff --git a/synapse/push/emailpusher.py b/synapse/push/emailpusher.py
index 3a13c7485a7d..b4b728adc547 100644
--- a/synapse/push/emailpusher.py
+++ b/synapse/push/emailpusher.py
@@ -26,11 +26,14 @@
 
 # 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 = 2 * 60 * 1000
+DELAY_BEFORE_MAIL_MS = 10 * 60 * 1000
 
-THROTTLE_START_MS = 2 * 60 * 1000
-THROTTLE_MAX_MS = (2 * 60 * 1000) * (2 ** 11)  # ~3 days
-THROTTLE_MULTIPLIER = 2
+# 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  # (2 * 60 * 1000) * (2 ** 11)  # ~3 days
+THROTTLE_MULTIPLIER = 6                # 10 mins, 1 hour, 6 hours, 24 hours
 
 # If no event triggers a notification for this long after the previous,
 # the throttle is released.
@@ -146,7 +149,18 @@ def _unsafe_process(self):
                 # *one* email updating the user on their notifications,
                 # we then consider all previously outstanding notifications
                 # to be delivered.
-                yield self.send_notification(unprocessed)
+
+                # debugging:
+                reason = {
+                    'room_id': push_action['room_id'],
+                    'now': self.clock.time_msec(),
+                    'received_at': received_at,
+                    'delay_before_mail_ms': 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']),
+                }
+
+                yield self.send_notification(unprocessed, reason)
 
                 yield self.save_last_stream_ordering_and_success(max([
                     ea['stream_ordering'] for ea in unprocessed
@@ -195,7 +209,8 @@ def room_ready_to_notify_at(self, room_id):
         """
         Determines whether throttling should prevent us from sending an email
         for the given room
-        Returns: True if we should send, False if we should not
+        Returns: The timestamp when we are next allowed to send an email notif
+        for this room
         """
         last_sent_ts = self.get_room_last_sent_ts(room_id)
         throttle_ms = self.get_room_throttle_ms(room_id)
@@ -244,8 +259,9 @@ def sent_notif_update_throttle(self, room_id, notified_push_action):
         )
 
     @defer.inlineCallbacks
-    def send_notification(self, push_actions):
+    def send_notification(self, push_actions, reason):
         logger.info("Sending notif email for user %r", self.user_id)
+
         yield self.mailer.send_notification_mail(
-            self.user_id, self.email, push_actions
+            self.user_id, self.email, push_actions, reason
         )
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index 2fd38a036aea..c2c2ca3fa7b2 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -92,7 +92,7 @@ def __init__(self, hs):
         )
 
     @defer.inlineCallbacks
-    def send_notification_mail(self, user_id, email_address, push_actions):
+    def send_notification_mail(self, user_id, email_address, push_actions, reason):
         raw_from = email.utils.parseaddr(self.hs.config.email_notif_from)[1]
         raw_to = email.utils.parseaddr(email_address)[1]
 
@@ -143,12 +143,17 @@ def _fetch_room_state(room_id):
             notifs_by_room, state_by_room, notif_events, user_id
         )
 
+        reason['room_name'] = calculate_room_name(
+            state_by_room[reason['room_id']], user_id, fallback_to_members=False
+        )
+
         template_vars = {
             "user_display_name": user_display_name,
             "unsubscribe_link": self.make_unsubscribe_link(),
             "summary_text": summary_text,
             "app_name": self.app_name,
             "rooms": rooms,
+            "reason": reason,
         }
 
         html_text = self.notif_template_html.render(**template_vars)