https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/5555-actionmailer-239-should-now-require-uri

--- lib/action_mailer/base.rb.orig	2010-09-05 10:56:52.424972729 +0200
+++ lib/action_mailer/base.rb	2010-09-05 10:56:59.760472595 +0200
@@ -247,6 +247,7 @@
   class Base
     include AdvAttrAccessor, PartContainer, Quoting, Utils
     if Object.const_defined?(:ActionController)
+      require 'uri'
       include ActionController::UrlWriter
       include ActionController::Layout
     end