title: What is the "plain" authentication_type in mailer?
body: <p>Looking at the <a href="http://guides.rubyonrails.org/action_mailer_basics.html#action-mailer-configuration" rel="nofollow">Rails Guides for action mailer</a>, what does the "plain" <code>authentication_type</code> mean in the action mailer <code>smtp_settings</code>?</p>
  
  <p>Does it mean that my password will be sent in the clear?
  (If it helps, I am using gmail as the smtp provider.)</p>