title: The recipient will be replaced with default from
body: <p>This is an strange problem,</p>
  
  <p>At first I could send my mail via mailgun,</p>
  
  <p>But now the expected recipient <code>bill.email</code> will be replaced with <code>me@#{ENV['mailgun_domain']}</code></p>
  
  <p>I totally have no idea. because the code not changed</p>
  
  <pre><code>class BillMailer &lt; ActionMailer::Base
    default from: "me@#{ENV['mailgun_domain']}"
    def confirm_bill(bill, cart)
      mail(to: bill.email, cc: "poc7667@gmail.com")
    end
  end
  </code></pre>
  
  <p>I printed the <code>mail</code> object, everything looks fine</p>
  
  <pre><code>#&lt;Mail::Message:70158682584200, Multipart: false, Headers: &lt;From: balance@4am-lesson.com&gt;, &lt;To: test_123@gmail.com&gt;, &lt;Cc: test_123@gmail.com&gt;, &lt;Subject: hihi&gt;, &lt;Mime-Version: 1.0&gt;, &lt;Content-Type: text/html&gt;&gt;
  </code></pre>
  
  <p>But when I checked the mailgun log, my recipient was replaced with <code>balance_coffe@sandboxc88b11b1bddf4594aad351f79e76d6ba.mailgun.org</code>, it supposed be my default sent from, I thought it a mailgun bug</p>
  
  <pre><code> "message": {
      "headers": {
        "to": "balance_coffe@sandboxc88b11b1bddf4594aad351f79e76d6ba.mailgun.org",
        "message-id": "20150503112244.C04DC5995993@Poc-MacBook-Pro-Retina-15-2013-late-2.local",
        "from": "MAILER-DAEMON@Poc-MacBook-Pro-Retina-15-2013-late-2.local (Mail Delivery System)",
        "subject": "Undelivered Mail Returned to Sender"
      },
      "attachments": [],
      "recipients": [
        "balance_coffe@sandboxc88b11b1bddf4594aad351f79e76d6ba.mailgun.org"
      ],
      "size": 20919
    },
    "recipient": "balance_coffe@sandboxc88b11b1bddf4594aad351f79e76d6ba.mailgun.org",
    "event": "accepted"
  </code></pre>