FEATURE: do not send notification emails to users who are included in the To and CC header of an incoming email

app/services/post_alerter.rb

@@ -392,13 +392,20 @@ class PostAlerter
       notification_data[:group_name] = group.name
     end
 
+    if original_post.via_email && (incoming_email = original_post.incoming_email)
+      skip_send_email = contains_email_address?(incoming_email.to_addresses, user) ||
+        contains_email_address?(incoming_email.cc_addresses, user)
+    else
+      skip_send_email = opts[:skip_send_email]
+    end
+
     # Create the notification
     user.notifications.create(notification_type: type,
                               topic_id: post.topic_id,
                               post_number: post.post_number,
                               post_action_id: opts[:post_action_id],
                               data: notification_data.to_json,
-                              skip_send_email: opts[:skip_send_email])
+                              skip_send_email: skip_send_email)
 
    if !existing_notification && NOTIFIABLE_TYPES.include?(type) && !user.suspended?
      # we may have an invalid post somehow, dont blow up
@@ -422,6 +429,11 @@ class PostAlerter
 
   end
 
+  def contains_email_address?(addresses, user)
+    return false if addresses.blank?
+    addresses.split(";").include?(user.email)
+  end
+
   def push_notification(user, payload)
     if SiteSetting.allow_user_api_key_scopes.split("|").include?("push") && SiteSetting.allowed_user_api_push_urls.present?
       clients = user.user_api_keys

spec/fabricators/incoming_email_fabricator.rb

@@ -1 +1,20 @@
-Fabricator(:incoming_email)
+Fabricator(:incoming_email) do
+  message_id "12345@example.com"
+  subject "Hello world"
+  from_address "foo@example.com"
+  to_addresses "someone@else.com"
+
+  raw <<~RAW
+    Return-Path: <foo@example.com>
+    From: Foo <foo@example.com>
+    To: someone@else.com
+    Subject: Hello world
+    Date: Fri, 15 Jan 2016 00:12:43 +0100
+    Message-ID: <12345@example.com>
+    Mime-Version: 1.0
+    Content-Type: text/plain; charset=UTF-8
+    Content-Transfer-Encoding: quoted-printable
+
+    The body contains "Hello world" too.
+  RAW
+end

spec/fabricators/post_fabricator.rb

@@ -133,3 +133,14 @@ Fabricator(:private_message_post, from: :post) do
   end
   raw "Ssshh! This is our secret conversation!"
 end
+
+Fabricator(:post_via_email, from: :post) do
+  incoming_email
+  via_email true
+
+  after_create do |post|
+    incoming_email.topic = post.topic
+    incoming_email.post = post
+    incoming_email.user = post.user
+  end
+end

spec/services/post_alerter_spec.rb

@@ -572,6 +572,61 @@ describe PostAlerter do
 
       expect(admin1.notifications.where(notification_type: Notification.types[:replied]).count).to eq(1)
     end
+
+    it "sends email notifications only to users not on CC list of incoming email" do
+      alice = Fabricate(:user, username: "alice", email: "alice@example.com")
+      bob = Fabricate(:user, username: "bob", email: "bob@example.com")
+      carol = Fabricate(:user,username: "carol", email: "carol@example.com", staged: true)
+      dave = Fabricate(:user, username: "dave", email: "dave@example.com", staged: true)
+      erin = Fabricate(:user, username: "erin", email: "erin@example.com")
+
+      topic = Fabricate(:private_message_topic, topic_allowed_users: [
+        Fabricate.build(:topic_allowed_user, user: alice),
+        Fabricate.build(:topic_allowed_user, user: bob),
+        Fabricate.build(:topic_allowed_user, user: carol),
+        Fabricate.build(:topic_allowed_user, user: dave),
+        Fabricate.build(:topic_allowed_user, user: erin)
+      ])
+      post = Fabricate(:post, user: alice, topic: topic)
+
+      TopicUser.change(alice.id, topic.id, notification_level: TopicUser.notification_levels[:watching])
+      TopicUser.change(bob.id, topic.id, notification_level: TopicUser.notification_levels[:watching])
+      TopicUser.change(erin.id, topic.id, notification_level: TopicUser.notification_levels[:watching])
+
+      email = Fabricate(:incoming_email,
+                        raw: <<~RAW,
+                          Return-Path: <bob@example.com>
+                          From: Bob <bob@example.com>
+                          To: meta+1234@discoursemail.com, dave@example.com
+                          CC: carol@example.com, erin@example.com
+                          Subject: Hello world
+                          Date: Fri, 15 Jan 2016 00:12:43 +0100
+                          Message-ID: <12345@example.com>
+                          Mime-Version: 1.0
+                          Content-Type: text/plain; charset=UTF-8
+                          Content-Transfer-Encoding: quoted-printable
+
+                          This post was created by email.
+                        RAW
+                        from_address: "bob@example.com",
+                        to_addresses: "meta+1234@discoursemail.com;dave@example.com",
+                        cc_addresses: "carol@example.com;erin@example.com")
+      reply = Fabricate(:post_via_email, user: bob, topic: topic, incoming_email: email, reply_to_post_number: 1)
+
+      NotificationEmailer.expects(:process_notification).with { |n| n.user_id == alice.id }.once
+      NotificationEmailer.expects(:process_notification).with { |n| n.user_id == bob.id }.never
+      NotificationEmailer.expects(:process_notification).with { |n| n.user_id == carol.id }.never
+      NotificationEmailer.expects(:process_notification).with { |n| n.user_id == dave.id }.never
+      NotificationEmailer.expects(:process_notification).with { |n| n.user_id == erin.id }.never
+
+      PostAlerter.post_created(reply)
+
+      expect(alice.notifications.count).to eq(1)
+      expect(bob.notifications.count).to eq(0)
+      expect(carol.notifications.count).to eq(1)
+      expect(dave.notifications.count).to eq(1)
+      expect(erin.notifications.count).to eq(1)
+    end
   end
 
   context "watching" do