title: Where do I put helper methods for ActionMailer views?
body: <p>I have a method that takes an array of strings and joins them so they do something like this:</p>
  
  <pre><code>&gt;&gt; my_arr
  =&gt; ["A", "B", "C"]
  &gt;&gt; and_join(my_arr)
  =&gt; "A, B, and C"
  </code></pre>
  
  <p>Which I'd like my mailer to have access to so I can output some information into an email. I can't seem to find a good place to put it and putting it in the application_helper.rb file and it doesn't find it there. Where should it go?</p>