title: Undefined method 'default_content_type=' in ActionMailer in Rails 3.2.1
body: <p>I added a system on my project to reset a user's password and send it to him via email in case he forgot it. It was working fine yesterday(when I implemented it). When I tried to fire up the server today, I got the following error.</p>
  
  <pre><code>=&gt; Booting WEBrick
  =&gt; Rails 3.2.1 application starting in development on http://0.0.0.0:3000
  =&gt; Call with -d to detach
  =&gt; Ctrl-C to shutdown server
  Exiting
  /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/actionmailer-3.2.1/lib/action_mailer/base.rb:437:in `method_missing': undefined method `default_content_type=' for ActionMailer::Base:Class (NoMethodError)
  from /Users/vinayshenoy/flo-server/config/environment.rb:7:in `&lt;top (required)&gt;'
  from /Users/vinayshenoy/flo-server/config.ru:4:in `require'
  from /Users/vinayshenoy/flo-server/config.ru:4:in `block in &lt;main&gt;'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/builder.rb:51:in `instance_eval'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/builder.rb:51:in `initialize'
  from /Users/vinayshenoy/flo-server/config.ru:1:in `new'
  from /Users/vinayshenoy/flo-server/config.ru:1:in `&lt;main&gt;'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/builder.rb:40:in `eval'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/builder.rb:40:in `parse_file'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/server.rb:200:in `app'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/server.rb:46:in `app'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/server.rb:301:in `wrapped_app'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/rack-1.4.1/lib/rack/server.rb:252:in `start'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/server.rb:70:in `start'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:55:in `block in &lt;top (required)&gt;'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:50:in `tap'
  from /Users/vinayshenoy/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:50:in `&lt;top (required)&gt;'
  from script/rails:6:in `require'
  from script/rails:6:in `&lt;main&gt;' 
  </code></pre>
  
  <p>This is my config/environment.rb file</p>
  
  <pre><code># Load the rails application
  require File.expand_path('../application', __FILE__)
  
  # Initialize the rails application
  FloServer::Application.initialize!
  
  ActionMailer::Base.default_content_type = "text/html"
  </code></pre>
  
  <p>If I comment out the <code>ActionMailer::Base.default_content_type = "text/html"</code> line, the server works without any problem. But without it, I can't send emails.</p>
  
  <p>I added this to config/environments/development.rb file yesterday</p>
  
  <pre><code>config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
  :address              =&gt; "smtp.gmail.com",
  :port                 =&gt; 587,
  :user_name            =&gt; 'username',
  :password             =&gt; 'password',
  :authentication       =&gt; 'plain',
  :enable_starttls_auto =&gt; true  }
  </code></pre>
  
  <p>I've tried restarting the Mac, running "bundle update" and reinstalling rails without any results.</p>
  
  <p>I'm using Rails 3.2.1 on Ruby 1.9.3. Please help.</p>