To whitelist an email address just means you add them to your approved senders' list. This tells your email client that you know this sender and trusts them, which will keep emails from this contact at the top of your inbox and out of the junk folder. There are a few ways you can do this.

Add the address to your contacts:

Add the email address that is sending you an email to your Contact List. Most email providers will usually deliver emails from addresses that are in your Contacts List.

If you find our emails in your "Promotions" Tab (Gmail users):

1. Go to your Promotions tab and locate an email from us there 
2. Simply drag this email over to the Primary tab of your inbox

Yahoo Mail Users:

When you open the email message, you should see a "+" symbol directly next to the From: and the Sender's Name. Click on the "+" symbol and then Add To Contacts. A pop-up should appear. Select Save. 

Outlook 2003 & Later Users:

In the list view of your emails, locate an email from us. Right-click on the email message in your inbox. Then select Junk E-mail from the contextual menu. Then click on Add Sends to Safe Senders List in that submenu.