title: ActionMailer throws an error while attaching files
body: <p>I have ActionMailer working and sending plain emails.
  But when I try to attach a file, I get: <code>#&lt;Encoding::UndefinedConversionError: "\xFF" from ASCII-8BIT to UTF-8&gt; - nil</code></p>
  
  <p>My snippet for doing that is:</p>
  
  <pre><code>mail(subject: "test test",
           from: "o@myemail.com",
           to: ["b@reciepient.com"],
           date: Time.now,
           content_type: "text/html",
           attachments[file[:filename]] =&gt; file[:data] )
  </code></pre>
  
  <p>Any suggestion what may go wrong?</p>
  
  <p>Thanks!</p>