module Roda::RodaPlugins::Mailer::InstanceMethods

def initialize(env)

as the default content_type for the email.
If this is an email request, set the mail object in the response, as well 
def initialize(env)
  super
  if mail = env['roda.mail']
    res = @_response
    res.mail = mail
    res.headers.delete('Content-Type')
  end
end