The Friends list contains the email addresses of people from whom you always want to receive mail, regardless of the content. Messages received from an address on your Friends list will be marked as friend regardless of whether or not the message resembles spam.
By default, the column containing the Friends list, Blacklist, and Filters tabs displays. To turn this column on and off, select the View menu and check or uncheck the Filter sidebar option.
To find out more about how to use your Friends list, see Managing the Friends list. To further customize your Friends list, Customizing the Friends list.