mt.rb

require "mail"

mail = Mail.new do
  to      'nicolas@test.lindsaar.net.au'
  from    'Mikel Lindsaar <mikel@test.lindsaar.net.au>'
  subject 'First multipart email sent with Mail'

  text_part do
    body 'Find my source code attached'
  end

  html_part do
    content_type 'text/html; charset=UTF-8'
    body 'Find my <b>source code</b> attached'
  end
  
  attachments['xxx'] = { mime_type: "bla", content: File.read(__FILE__) }
end

puts mail.to_s