I was using smart host for my regular smtp mail (exim). The new beta version upgrades the smart host automatically. You cannot use the automatically system generated smart host for notifier.
I tried modifying the smarthost setting. Very interesting, you cannot dnd an existing network into the smarthost setting. You can create the same value as a dns host which still does not transmit messages.
Thanks for your Feedback, again. Probably the DNS resolver needed a little bit more time to resolve your DNS host object. I guess DNS host objects can only be used when the name resolution was successful.