Add custom headers for email messages

See http://meta.discourse.org/t/custom-headers-in-emails-site-settings/7480

app/models/site_setting.rb

@@ -129,6 +129,7 @@ class SiteSetting < ActiveRecord::Base
 
   # we need to think of a way to force users to enter certain settings, this is a minimal config thing
   setting(:notification_email, 'info@discourse.org')
+  setting(:email_custom_headers, 'Precedence: bulk|Auto-Submitted: auto-generated')
 
   setting(:allow_index_in_robots_txt, true)
 

config/locales/server.en.yml

@@ -477,6 +477,7 @@ en:
     apple_touch_icon_url: "Icon used for Apple touch devices. Recommended size is 144px by 144px."
 
     notification_email: "The return email address used when sending system emails such as notifying users of lost passwords, new accounts etc"
+    email_custom_headers: "A pipe-delimited list of custom email headers"
     use_ssl: "Should the site be accessible via SSL? (NOT IMPLEMENTED, EXPERIMENTAL)"
     best_of_score_threshold: "The minimum score of a post to be included in the 'best of'"
     best_of_posts_required: "Minimum posts in a topic before 'best of' mode is enabled"

lib/email/message_builder.rb

@@ -75,6 +75,19 @@ module Email
         result['Reply-To'] = from_value
       end
 
+      result.merge(MessageBuilder.custom_headers(SiteSetting.email_custom_headers))
+    end
+
+    def self.custom_headers(string)
+      result = {}
+      string.split('|').each { |item|
+        header = item.split(':', 2)
+        if header.length == 2
+          name = header[0].strip
+          value = header[1].strip
+          result[name] = value if name.length > 0 && value.length > 0
+        end
+      }
       result
     end
 

spec/components/email/message_builder_spec.rb

@@ -75,6 +75,17 @@ describe Email::MessageBuilder do
 
   end
 
+  context "custom headers" do
+
+    let(:custom_headers_string) { " Precedence : bulk | :: | No-colon | No-Value: | Multi-colon : : value : : | Auto-Submitted : auto-generated " }
+    let(:custom_headers_result) { { "Precedence" => "bulk", "Multi-colon" => ": value : :", "Auto-Submitted" => "auto-generated" } }
+
+    it "custom headers builder" do
+      expect(Email::MessageBuilder.custom_headers(custom_headers_string)).to eq(custom_headers_result)
+    end
+
+  end
+
   context "header args" do
 
     let(:message_with_header_args) { Email::MessageBuilder.new(to_address,