FEATURE: limit daily emails per user to 100 per day via site setting

- controlled via max_emails_per_day_per_user, 0 to disable
- when limit is reached user is warned

app/jobs/regular/notify_mailing_list_subscribers.rb

@@ -35,8 +35,19 @@ module Jobs
       users.each do |user|
         if Guardian.new(user).can_see?(post)
           begin
-            message = UserNotifications.mailing_list_notify(user, post)
-            Email::Sender.new(message, :mailing_list, user).send if message
+            if EmailLog.reached_max_emails?(user)
+              EmailLog.create!(
+                email_type: 'mailing_list',
+                to_address: user.email,
+                user_id: user.id,
+                post_id: post.id,
+                skipped: true,
+                skipped_reason: "[MailingList] #{I18n.t('email_log.exceeded_limit')}"
+              )
+            else
+              message = UserNotifications.mailing_list_notify(user, post)
+              Email::Sender.new(message, :mailing_list, user).send if message
+            end
           rescue => e
             Discourse.handle_job_exception(e, error_context(args, "Sending post to mailing list subscribers", { user_id: user.id, user_email: user.email }))
           end

app/jobs/regular/user_email.rb

@@ -113,6 +113,10 @@ module Jobs
         email_args[:new_email] = user.email
       end
 
+      if EmailLog.reached_max_emails?(user)
+        return skip_message(I18n.t('email_log.exceeded_limit'))
+      end
+
       message = UserNotifications.send(type, user, email_args)
 
       # Update the to address if we have a custom one

app/mailers/user_notifications.rb

@@ -317,6 +317,11 @@ class UserNotifications < ActionMailer::Base
       end
     end
 
+    reached_limit = SiteSetting.max_emails_per_day_per_user > 0
+    reached_limit &&= (EmailLog.where(user_id: user.id, skipped: false)
+                            .where('created_at > ?', 1.day.ago)
+                            .count) >= (SiteSetting.max_emails_per_day_per_user-1)
+
     topic_excerpt = ""
     if opts[:use_template_html]
       topic_excerpt = post.excerpt.gsub("\n", " ") if post.is_first_post? && post.excerpt
@@ -326,6 +331,7 @@ class UserNotifications < ActionMailer::Base
         template: 'email/notification',
         format: :html,
         locals: { context_posts: context_posts,
+                  reached_limit: reached_limit,
                   post: post,
                   in_reply_to_post: in_reply_to_post,
                   classes: RTL.new(user).css_class
@@ -339,10 +345,11 @@ class UserNotifications < ActionMailer::Base
       template << "_staged" if user.staged?
     end
 
+
     email_opts = {
       topic_title: title,
       topic_excerpt: topic_excerpt,
-      message: email_post_markdown(post),
+      message: email_post_markdown(post) + (reached_limit ? "\n\n#{I18n.t "user_notifications.reached_limit", count: SiteSetting.max_emails_per_day_per_user}" : ""),
       url: post.url,
       post_id: post.id,
       topic_id: post.topic_id,

app/models/email_log.rb

@@ -13,6 +13,16 @@ class EmailLog < ActiveRecord::Base
     User.where(id: user_id).update_all("last_emailed_at = CURRENT_TIMESTAMP") if user_id.present? && !skipped
   end
 
+  def self.reached_max_emails?(user)
+    return false if SiteSetting.max_emails_per_day_per_user == 0
+
+    count = sent.where('created_at > ?', 1.day.ago)
+        .where(user_id: user.id)
+        .count
+
+    count >= SiteSetting.max_emails_per_day_per_user
+  end
+
   def self.count_per_day(start_date, end_date)
     sent.where("created_at BETWEEN ? AND ?", start_date, end_date)
         .group("DATE(created_at)")

app/views/email/notification.html.erb

@@ -10,12 +10,12 @@
   <% end %>
 
   <% if in_reply_to_post.present? %>
-    <h4 class='.previous-discussion'><%= t "user_notifications.in_reply_to" %></h4>
+    <h4 class='previous-discussion'><%= t "user_notifications.in_reply_to" %></h4>
     <%= render partial: 'email/post', locals: { post: in_reply_to_post, use_excerpt: true} %>
   <% end %>
 
   <% if context_posts.present? %>
-    <h4 class='.previous-discussion'><%= t "user_notifications.previous_discussion" %></h4>
+    <h4 class='previous-discussion'><%= t "user_notifications.previous_discussion" %></h4>
     <% context_posts.each do |p| %>
       <%= render partial: 'email/post', locals: { post: p, use_excerpt: false } %>
     <% end %>
@@ -23,6 +23,9 @@
 
   <hr>
 
+  <% if reached_limit %>
+    <div class='footer'><%= t "user_notifications.reached_limit", count: SiteSetting.max_emails_per_day_per_user %></div>
+  <% end %>
   <div class='footer'>%{respond_instructions}</div>
   <div class='footer'>%{unsubscribe_link}%{unsubscribe_via_email_link}</div>
 

config/locales/server.en.yml

@@ -1161,6 +1161,7 @@ en:
     unsubscribe_via_email_footer: "Attach an unsubscribe link to the footer of sent emails"
 
     delete_email_logs_after_days: "Delete email logs after (N) days. 0 to keep indefinitely"
+    max_emails_per_day_per_user: "Maximum number of emails to send users per day. 0 to disable the limit"
 
     manual_polling_enabled: "Push emails using the API for email replies."
     pop3_polling_enabled: "Poll via POP3 for email replies."
@@ -2037,6 +2038,9 @@ en:
 
   user_notifications:
     previous_discussion: "Previous Replies"
+    reached_limit:
+      one: "WARNING: you reached the limit of daily emails. Further email notifications will be suppressed."
+      other: "WARNING: you reached the limit of %{count} daily emails. Further email notifications will be suppressed."
     in_reply_to: "In Reply To"
     unsubscribe:
       title: "Unsubscribe"
@@ -2363,6 +2367,7 @@ en:
     post_deleted: "post was deleted by the author"
     user_suspended: "user was suspended"
     already_read: "user has already read this post"
+    exceeded_limit: "Exceeded max_emails_per_day_per_user"
     message_blank: "message is blank"
     message_to_blank: "message.to is blank"
     text_part_body_blank: "text_part.body is blank"

config/site_settings.yml

@@ -559,6 +559,7 @@ email:
   delete_email_logs_after_days:
     default: 365
     min: 0
+  max_emails_per_day_per_user: 100
 
 files:
   max_image_size_kb: 3072

spec/jobs/notify_mailing_list_subscribers_spec.rb

@@ -3,9 +3,34 @@ require "rails_helper"
 describe Jobs::NotifyMailingListSubscribers do
 
   context "with mailing list on" do
-    before { SiteSetting.stubs(:default_email_mailing_list_mode).returns(true) }
+    before { SiteSetting.default_email_mailing_list_mode = true }
     let(:user) { Fabricate(:user) }
 
+    context "SiteSetting.max_emails_per_day_per_user" do
+
+      it 'stops sending mail once limit is reached' do
+        SiteSetting.max_emails_per_day_per_user = 2
+        post = Fabricate(:post)
+
+        user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+        user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+
+        Jobs::NotifyMailingListSubscribers.new.execute(post_id: post.id)
+        expect(EmailLog.where(user_id: user.id, skipped: true).count).to eq(1)
+      end
+    end
+
+    context "totally skipped if mailing list mode disabled" do
+
+      it "sends no email to the user" do
+        SiteSetting.disable_mailing_list_mode = true
+
+        post = Fabricate(:post)
+        Jobs::NotifyMailingListSubscribers.new.execute(post_id: post.id)
+        expect(EmailLog.count).to eq(0)
+      end
+    end
+
     context "with a valid post" do
       let!(:post) { Fabricate(:post, user: user) }
 

spec/jobs/user_email_spec.rb

@@ -193,6 +193,17 @@ describe Jobs::UserEmail do
         Jobs::UserEmail.new.execute(type: :user_mentioned, user_id: user.id, notification_id: notification.id)
       end
 
+      it "does not send notification if limit is reached" do
+        SiteSetting.max_emails_per_day_per_user = 2
+
+        user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+        user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+
+        Jobs::UserEmail.new.execute(type: :user_mentioned, user_id: user.id, notification_id: notification.id, post_id: post.id)
+
+        expect(EmailLog.where(user_id: user.id, skipped: true).count).to eq(1)
+      end
+
       it "doesn't send the mail if the user is using mailing list mode" do
         Email::Sender.any_instance.expects(:send).never
         user.user_option.update_column(:mailing_list_mode, true)
@@ -205,7 +216,7 @@ describe Jobs::UserEmail do
         # When post does not have a topic
         post = Fabricate(:post)
         post.topic.destroy
-        Jobs::UserEmail.new.execute(type: :user_mentioned, user_id: user.id, notification_type: "posted", post_id: post)
+        Jobs::UserEmail.new.execute(type: :user_mentioned, user_id: user.id, notification_type: "posted", post_id: post.id)
       end
 
       it "doesn't send the email if the post has been user deleted" do

spec/mailers/user_notifications_spec.rb

@@ -243,6 +243,31 @@ describe UserNotifications do
     end
   end
 
+
+  it 'adds a warning when mail limit is reached' do
+    SiteSetting.max_emails_per_day_per_user = 2
+    user = Fabricate(:user)
+    user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id, skipped: false)
+
+    post = Fabricate(:post)
+    reply = Fabricate(:post, topic_id: post.topic_id)
+
+    notification = Fabricate(:notification, topic_id: post.topic_id, post_number: reply.post_number,
+                             user: post.user, data: {original_username: 'bob'}.to_json)
+
+    mail = UserNotifications.user_replied(
+      user,
+      post: reply,
+      notification_type: notification.notification_type,
+      notification_data_hash: notification.data_hash
+    )
+
+    # WARNING: you reached the limit of 100 email notifications per day. Further emails will be suppressed.
+    # Consider watching less topics or disabling mailing list mode.
+    expect(mail.html_part.to_s).to match("WARNING: ")
+    expect(mail.body.to_s).to match("WARNING: ")
+  end
+
   def expects_build_with(condition)
     UserNotifications.any_instance.expects(:build_email).with(user.email, condition)
     mailer = UserNotifications.send(mail_type, user,

spec/models/email_log_spec.rb

@@ -26,6 +26,21 @@ describe EmailLog do
     end
   end
 
+  describe '#reached_max_emails?' do
+    it "tracks when max emails are reached" do
+      SiteSetting.max_emails_per_day_per_user = 2
+      user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id, skipped: true)
+      user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+      user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id, created_at: 3.days.ago)
+
+      expect(EmailLog.reached_max_emails?(user)).to eq(false)
+
+      user.email_logs.create(email_type: 'blah', to_address: user.email, user_id: user.id)
+
+      expect(EmailLog.reached_max_emails?(user)).to eq(true)
+    end
+  end
+
   describe '#count_per_day' do
     it "counts sent emails" do
       user.email_logs.create(email_type: 'blah', to_address: user.email)