Fortimail - Authentication integration with Zimbra

Guys, good morning. I need some help, the thing is, i have a Zimbra as mail server. The clients is using it. And i'm using now the Fortimail as an Antispam server.

So, wat I wanna do is that the user can enter in the Fortimail to release spam and things like that, using his credentials from Zimbra. I already configured the authentication, but seems that is not working, so you guys have anything that may help me?