title: Rails ActionMailer with multiple SMTP servers
body: <p>I have a need to use two different smtp servers in a Rails application. It appears that the way ActionMailer is constructed, it is not possible to have different smtp_settings for 
  a subclass. I could reload the smtp settings for each mailer class whenever a message is being sent, but that messes up the ExceptionNotifier plugin which is outside my control (unless I mess with it too). Does anyone have a solution/plugin for something like 
  this?</p>
  
  <p>Ideally I would like to have</p>
  
  <pre><code>class UserMailer &lt; ActionMailer::Base; end
  </code></pre>
  
  <p>and then set in environment.rb</p>
  
  <pre><code>ActionMailer::Base.smtp_settings = standard_smtp_settings
  UserMailer.smtp_settings = user_smtp_settings
  </code></pre>
  
  <p>Thus, most of my mailers including ExceptionNotifier would pickup the default settings, but the UserMailer would use a paid relay service.</p>