add list unsubscribe

app/mailers/invite_mailer.rb

@@ -1,6 +1,7 @@
 require_dependency 'email_builder'
 
 class InviteMailer < ActionMailer::Base
+  default charset: 'UTF-8'
   include EmailBuilder
 
   def send_invite(invite)

app/mailers/test_mailer.rb

@@ -1,6 +1,7 @@
 require_dependency 'email_builder'
 
 class TestMailer < ActionMailer::Base
+  default charset: 'UTF-8'
   include EmailBuilder
 
   def send_test(to_address)

app/mailers/user_notifications.rb

@@ -2,6 +2,8 @@ require_dependency 'markdown_linker'
 require_dependency 'email_builder'
 
 class UserNotifications < ActionMailer::Base
+  default charset: 'UTF-8'
+
   include EmailBuilder
 
   def signup(user, opts={})

lib/email_builder.rb

@@ -12,6 +12,7 @@ module EmailBuilder
     if params[:add_unsubscribe_link]
       body << "\n"
       body << I18n.t("unsubscribe_link", params)
+      headers 'List-Unsubscribe' => "<#{params[:user_preferences_url]}>"
     end
 
     mail_args = {