module Roda::RodaPlugins::Mailer::InstanceMethods

def add_file(*a, &block)

can access the attachment via response.mail_attachments.last.
If a block is given, the block is called after the file has been added, and you
Delay adding a file to the message until after the message body has been set.
def add_file(*a, &block)
  response.mail_attachments << [a, block]
  nil
end