
If someone copies the production Zuul configuration, they may end up sending emails as jenkins@o.o. Configure our hosts to only accept email with an envelope sender or From header of jenkins@.o.o if the connecting host is zuul.openstack.org (or localhost, to handle the case of exim running on zuul.o.o itself). Change-Id: Ic92bb39659689347fea1744ee8c1b47ef21858b0