There is a Safe List in the Comcast webmail. On the Inbox page click on the gear icon in the upper right corner of the page, then on Settings>>>>>>>Advanced Settings. There you will see the option to enable the list. HOWEVER---------understand that if you do, you will only get emails from contacts you deliberately put on that list---------------nothing else will get to your inbox. It's not a "whitelist" in the sense you may think it is.