It is no more needed, I believe

config/initializers/action_mailer_extensions.rb

@@ -1,47 +0,0 @@
-# Redmine plugin for Document Management System "Features"
-#
-# Copyright (C) 2011   Vít Jonáš <vit.jonas@gmail.com>
-#
-# This program is free software; you can redistribute it and/or
-# modify it under the terms of the GNU General Public License
-# as published by the Free Software Foundation; either version 2
-# of the License, or (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program; if not, write to the Free Software
-# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.%>
-
-module ActionMailer
-  class Base
-    class_inheritable_accessor :view_paths
-    
-    def self.prepend_view_path(path)
-      view_paths.unshift(*path)
-      ActionView::TemplateFinder.process_view_paths(path)
-    end
-
-    def self.append_view_path(path)
-      view_paths.push(*path)
-      ActionView::TemplateFinder.process_view_paths(path)
-    end
-
-    private
-    def self.view_paths
-      @@view_paths ||= [template_root]
-    end
-    
-    def view_paths
-      self.class.view_paths
-    end
-    
-    def initialize_template_class(assigns)
-      ActionView::Base.new(view_paths, assigns, self)
-    end
-
-  end
-end

lib/redmine_dmsf.rb

@@ -57,10 +57,3 @@ require 'redmine_dmsf/hooks/views/my_account_view_hooks'
 
 # Macros
 require 'redmine_dmsf/macros'
-
-module RedmineDmsf
-end
-
-# Add the plugin view folder into ActionMailer's paths to search
-ActionMailer::Base.append_view_path(File.expand_path(
-    File.dirname(__FILE__) + '/../app/views'))