diff --git a/app/mailers/user_notifications.rb b/app/mailers/user_notifications.rb
index 4232a647972..253e94d9a1c 100644
--- a/app/mailers/user_notifications.rb
+++ b/app/mailers/user_notifications.rb
@@ -83,26 +83,33 @@ class UserNotifications < ActionMailer::Base
 
   def user_replied(user, opts)
     opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
     notification_email(user, opts)
   end
 
   def user_quoted(user, opts)
     opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
     notification_email(user, opts)
   end
 
   def user_mentioned(user, opts)
     opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
     notification_email(user, opts)
   end
 
   def user_posted(user, opts)
     opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
+    opts[:add_re_to_subject] = true
     notification_email(user, opts)
   end
 
   def user_private_message(user, opts)
     opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
+    opts[:add_re_to_subject] = true
 
     # We use the 'user_posted' event when you are emailed a post in a PM.
     opts[:notification_type] = 'posted'
@@ -116,6 +123,8 @@ class UserNotifications < ActionMailer::Base
       post: post,
       from_alias: post.user.username,
       allow_reply_by_email: true,
+      use_site_subject: true,
+      add_re_to_subject: true,
       notification_type: "posted",
       user: user
     )
@@ -163,12 +172,16 @@ class UserNotifications < ActionMailer::Base
 
     title = @notification.data_hash[:topic_title]
     allow_reply_by_email = opts[:allow_reply_by_email] unless user.suspended?
+    use_site_subject = opts[:use_site_subject]
+    add_re_to_subject = opts[:add_re_to_subject]
 
     send_notification_email(
       title: title,
       post: @post,
       from_alias: username,
       allow_reply_by_email: allow_reply_by_email,
+      use_site_subject: use_site_subject,
+      add_re_to_subject: add_re_to_subject,
       notification_type: notification_type,
       user: user
     )
@@ -179,6 +192,8 @@ class UserNotifications < ActionMailer::Base
     post = opts[:post]
     title = opts[:title]
     allow_reply_by_email = opts[:allow_reply_by_email]
+    use_site_subject = opts[:use_site_subject]
+    add_re_to_subject = opts[:add_re_to_subject] && post.post_number > 1
     from_alias = opts[:from_alias]
     notification_type = opts[:notification_type]
     user = opts[:user]
@@ -224,6 +239,8 @@ class UserNotifications < ActionMailer::Base
       username: from_alias,
       add_unsubscribe_link: true,
       allow_reply_by_email: allow_reply_by_email,
+      use_site_subject: use_site_subject,
+      add_re_to_subject: add_re_to_subject,
       private_reply: post.topic.private_message?,
       include_respond_instructions: !user.suspended?,
       template: template,
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index e2aef5a6cd1..1ad099e1e2b 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -690,6 +690,7 @@ en:
 
     notification_email: "The from: email address used when sending all essential system emails. The domain specified here must have SPF, DKIM and reverse PTR records set correctly for email to arrive."
     email_custom_headers: "A pipe-delimited list of custom email headers"
+    email_subject: "Subject format for standard emails."
     use_https: "Should the full url for the site (Discourse.base_url) be http or https? DO NOT ENABLE THIS UNLESS HTTPS IS ALREADY SET UP AND WORKING!"
     summary_score_threshold: "The minimum score required for a post to be included in 'Summarize This Topic'"
     summary_posts_required: "Minimum posts in a topic before 'Summarize This Topic' is enabled"
@@ -1576,6 +1577,9 @@ en:
 
   unsubscribe_link: "To unsubscribe from these emails, visit your [user preferences](%{user_preferences_url})."
 
+  subject_re: "Re: "
+  subject_pm: "[PM] "
+
   user_notifications:
     previous_discussion: "Previous Replies"
     unsubscribe:
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 8bcf1441904..1116324644b 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -390,6 +390,7 @@ email:
     default: 7
     enum: 'DigestEmailSiteSetting'
   email_custom_headers: 'Auto-Submitted: auto-generated'
+  email_subject: '%{optional_re}[%{site_name}] %{optional_pm}%{topic_title}'
   reply_by_email_enabled: false
   reply_by_email_address: ''
   pop3_polling_enabled: false
diff --git a/lib/email/message_builder.rb b/lib/email/message_builder.rb
index b488bff4578..ed8ea0b7567 100644
--- a/lib/email/message_builder.rb
+++ b/lib/email/message_builder.rb
@@ -40,8 +40,16 @@ module Email
     end
 
     def subject
-      subject = @opts[:subject]
-      subject = I18n.t("#{@opts[:template]}.subject_template", template_args) if @opts[:template]
+      if @opts[:use_site_subject]
+        subject = String.new(SiteSetting.email_subject)
+        subject.gsub!("%{site_name}", @template_args[:site_name])
+        subject.gsub!("%{optional_re}", @opts[:add_re_to_subject] ? I18n.t('subject_re', template_args) : '')
+        subject.gsub!("%{optional_pm}", @opts[:private_reply] ? I18n.t('subject_pm', template_args) : '')
+        subject.gsub!("%{topic_title}", @template_args[:topic_title]) if @template_args[:topic_title] # must be last for safety
+      else
+        subject = @opts[:subject]
+        subject = I18n.t("#{@opts[:template]}.subject_template", template_args) if @opts[:template]
+      end
       subject
     end
 
diff --git a/spec/mailers/user_notifications_spec.rb b/spec/mailers/user_notifications_spec.rb
index d7bb4b45888..0f612a87403 100644
--- a/spec/mailers/user_notifications_spec.rb
+++ b/spec/mailers/user_notifications_spec.rb
@@ -104,6 +104,53 @@ describe UserNotifications do
     end
   end
 
+  describe '.user_posted' do
+    let(:post) { Fabricate(:post) }
+    let(:response) { Fabricate(:post, topic: post.topic)}
+    let(:user) { Fabricate(:user) }
+    let(:notification) { Fabricate(:notification, user: user) }
+
+    it 'generates a correct email' do
+      mail = UserNotifications.user_posted(response.user, post: response, notification: notification)
+
+      # subject should include "Re:"
+      expect(mail.subject).to match("Re:")
+
+      # 2 respond to links cause we have 1 context post
+      mail.html_part.to_s.scan(/To respond/).count.should == 2
+
+      # 1 unsubscribe link
+      mail.html_part.to_s.scan(/To unsubscribe/).count.should == 1
+
+      # side effect, topic user is updated with post number
+      tu = TopicUser.get(post.topic_id, response.user)
+      tu.last_emailed_post_number.should == response.post_number
+    end
+  end
+
+  describe '.user_private_message' do
+    let(:topic) { Fabricate(:private_message_topic) }
+    let(:response) { Fabricate(:post, topic: topic)}
+    let(:user) { Fabricate(:user) }
+    let(:notification) { Fabricate(:notification, user: user) }
+
+    it 'generates a correct email' do
+      mail = UserNotifications.user_private_message(response.user, post: response, notification: notification)
+
+      # subject should include "[PM]"
+      expect(mail.subject).to match("[PM]")
+
+      # 1 respond to link
+      mail.html_part.to_s.scan(/To respond/).count.should == 1
+
+      # 1 unsubscribe link
+      mail.html_part.to_s.scan(/To unsubscribe/).count.should == 1
+
+      # side effect, topic user is updated with post number
+      tu = TopicUser.get(topic.id, response.user)
+      tu.last_emailed_post_number.should == response.post_number
+    end
+  end
 
   def expects_build_with(condition)
     UserNotifications.any_instance.expects(:build_email).with(user.email, condition)
@@ -126,7 +173,6 @@ describe UserNotifications do
     end
   end
 
-
   shared_examples "notification email building" do
     let(:post) { Fabricate(:post, user: user) }
     let(:mail_type) { "user_#{notification_type}"}