Using Pony to send email with attachments

I have a script that I'm using to try to send an email with an
attachment but for some reason I can't get both the HTML part of the
email to show at the sametime as the attachment to be in the email.

Here is my code

[code]
Pony.mail(
        :to => to,
        :from => 'Me <me@me.com>',
        :subject => html_entity_decoder.decode(options[:subject]),
        :html_body => "#{options[:body]}".html_safe,
        :attachments => {File.basename("#{attachment}") =>
File.read("#{attachment}")},
        :headers => { "Content-Type" => "multipart/mixed",
"Content-Transfer-Encoding" => "base64", "Content-Disposition" =>
"attachment" },
        :via => :smtp,
        :via_options => {
          :address => ADDRESS,
          :port => '25',
          :enable_starttls_auto => true,
          :user_name => USERNAME,
          :password => PWD,
          :authentication => :plain,
          :domain => DOMAIN
          }
      )
[/code]

I have no idea what is wrong and I have followed all of the
tutorials/examples out there on google but nothing has worked