Whitelisting not working

Hello,

I'm trying to whitelist an IP/Netmask on my Fortigate 100E, Firmware version 6.0.4, but for some reason emails are still being blocked.

I've read that maybe I have to enable smtp-spamhdrip (by default is disabled) in CLI, but I don't know how to do it. 

Can you help me? 

Thank you