Tried that, setting Zimbra as the secondary...did not work..I think I know why but am not sure..
In order to hide the @zimbra.clientdomain.com from showing when mail was sent..we created the domain "clientdomain" so we have alias
user@clientdomain.com..thus creating a local account and from what I understand you cannot send local accounts through a relay smtp...everything worked until we created the alias(local account/domain)
maybe I am missing something? or I am just trying to do the impossible..