'Prepare to resend messages later.
This errback function runs when no mail exchange server for the domain
can be found.
@type failure: L{Failure}
@param failure: The reason the mail exchange lookup failed.
@type factory: L{SMTPManagedRelayerFactory}
@param factory: A factory which can create a relayer for the mail
exchange server.
@type domain: L{bytes}
@param domain: A domain.'

def _ebExchange(self, failure, factory, domain):

    log.err(('Error    setting    up    managed    relay    factory    for    ' + domain))
    log.err(failure)
    def setWaiting(queue, messages):
        map(queue.setWaiting, messages)
    from twisted.internet import reactor
    reactor.callLater(30, setWaiting, self.queue, self.managed[factory])
    del self.managed[factory]
