In an IronPort, the “WHITELIST” is sender group is linked to the TRUSTED Mail Flow Policy. The TRUSTED policy contains reduced restrictions and is not scanned for Spam. Note: IronPort reputation IP filters are still in affect, however the false positive rate on the reputation based filtering is less than one in one million.
To add an email domain to the Whitelist sender group, click Mail Policies > HAT Overview
Click Add Sender
Enter the email address domain or IP Address of the senders mail server and click Submit
Remember to Commit Changes
That should do it, I hope you found this post helpful for using the WhiteList feature of the IronPort.