title: ActionMailer pass local variables to the erb template
body: <p>I know I could define instance variables e.g:</p>
  
  <pre><code>def user_register(username, email)
    @username = username
    @email = email
  
    mail(:to =&gt; email, :subject =&gt; "Welcome!", :template_name =&gt; "reg_#{I18n.locale}")
  end
  </code></pre>
  
  <p>But, is there a way to use <strong>local</strong> variables instead, just like passing <em>:locals</em> to partials?</p>