To do this you have to configure spam assassin inside your account's Cpanel interface. Here are the steps.
1.> Log into Cpanel for your account
2.> Under the "Mail" section click on the "Spam Assassin" icon.
3.> Near the bottom, click on "Configure SpamAssassin"
4.> Scroll down till you see the forms labeled "whitelist_from". There you can type in the email address which you want to be able to receive mail from. If there is no specific address you can use a * as a wildcard like this.
Once this is finished click "Save" at the bottom of the page and it will configure Spam Assassin to let through emails marked with that address.