Adds a List-Id header to outgoing mail

lib/email/sender.rb

@@ -7,6 +7,7 @@
 # It also adds an HTML part for the plain text body
 #
 require_dependency 'email/renderer'
+require 'uri'
 
 module Email
   class Sender
@@ -45,6 +46,9 @@ module Email
                                to_address: to_address,
                                user_id: @user.try(:id))
 
+
+      @message.header['List-Id'] = Email::Sender.list_id_for(SiteSetting.title, Discourse.base_url)
+
       add_header_to_log('X-Discourse-Reply-Key', email_log, :reply_key)
       add_header_to_log('X-Discourse-Post-Id', email_log, :post_id)
       add_header_to_log('X-Discourse-Topic-Id', email_log, :topic_id)
@@ -62,6 +66,20 @@ module Email
 
     end
 
+    def self.list_id_for(site_name, base_url)
+
+      host = "localhost"
+      if base_url.present?
+        begin
+          uri = URI.parse(base_url)
+          host = uri.host.downcase if uri.host.present?
+        rescue URI::InvalidURIError
+        end
+      end
+
+      "\"#{site_name.gsub(/\"/, "'")}\" <#{Slug.for(site_name)}.#{host}>"
+    end
+
     private
 
     def add_header_to_log(name, email_log, email_log_field)

spec/components/email/sender_spec.rb

@@ -20,6 +20,34 @@ describe Email::Sender do
     Email::Sender.new(message, :hello).send
   end
 
+  context "list_id_for" do
+
+    it "joins the host and forum name" do
+      Email::Sender.list_id_for("myforum", "http://mysite.com").should == '"myforum" <myforum.mysite.com>'
+    end
+
+    it "uses localhost when no host is present" do
+      Email::Sender.list_id_for("myforum", nil).should == '"myforum" <myforum.localhost>'
+    end
+
+    it "uses localhost with a weird host" do
+      Email::Sender.list_id_for("Fun", "this is not a real host").should == '"Fun" <fun.localhost>'
+    end
+
+    it "removes double quotes from names" do
+      Email::Sender.list_id_for('Quoted "Forum"', 'http://quoted.com').should == '"Quoted \'Forum\'" <quoted-forum.quoted.com>'
+    end
+
+    it "converts the site name to lower case and removes spaces" do
+      Email::Sender.list_id_for("Robin's cool Forum!", "http://robin.com").should == '"Robin\'s cool Forum!" <robins-cool-forum.robin.com>'
+    end
+
+    it "downcases host names" do
+      Email::Sender.list_id_for("cool", "http://ForumSite.com").should == '"cool" <cool.forumsite.com>'
+    end
+
+  end
+
   context 'with a valid message' do
 
     let(:reply_key) { "abcd" * 8 }
@@ -38,6 +66,11 @@ describe Email::Sender do
       email_sender.send
     end
 
+    it "adds a List-Id header to identify the forum" do
+      email_sender.send
+      message.header['List-Id'].should be_present
+    end
+
     context 'email logs' do
       let(:email_log) { EmailLog.last }