class Mail::AttachmentsList

mail.attachments[1].filename #=> 'test.jpg'
mail.attachments['test.png'].filename #=> 'test.png'

mail.attachments['test.jpg'] = File.read('test.jpg')
mail.attachments['test.png'] = File.read('test.png')

Returns the attachment by filename or at index.

def [](index_value)
  if index_value.is_a?(Fixnum)
    self.fetch(index_value)
  else
    self.select { |a| a.filename == index_value }.first
  end
end