title: RestClient mailgun error "message": "'from' parameter is missing"
body: <p>I am using RestClient in my rails app to send emails. 
  The following Curl command works: </p>
  
  <pre><code>    curl -s "https://api:key-XYZ@api.mailgun.net/v2/sandbox30000.mailgun.org/messages" \
      -F from='Mailgun Sandbox &lt;postmaster@sandbox30000.mailgun.org&gt;' \
      -F to='me &lt;my-email-id@gmail.com&gt;'\
      -F subject='Hello XYZ' \
      -F text='Congratulations, you just sent an email with Mailgun!  You are truly awesome!'
  </code></pre>
  
  <p>But when I try the same using RestClient, I get the following error message:</p>
  
  <pre><code>    error response !!{
        "message": "'from' parameter is missing"
      }
  </code></pre>
  
  <p>error message  !!400 Bad Request </p>
  
  <p>RestClient call: </p>
  
  <pre><code>    RestClient::Request.execute(
      :url =&gt; "https://api:key-XYZ@api.mailgun.net/v2/sandbox0000.mailgun.org/messages",
      :method =&gt; :post,
      :from =&gt; 'Mailgun Sandbox &lt;postmaster@sandbox30000.mailgun.org&gt;',
      :sender =&gt; 'Mailgun Sandbox &lt;postmaster@sandbox30000.mailgun.org&gt;',
      :to =&gt; "my-email-id@gmail.com",
      :subject =&gt; "Hello XYZ",
      :text =&gt; "Text body",
      :"h:X-My-Header" =&gt; "www/mailgun-email-send",
      :verify_ssl =&gt; false)
  </code></pre>