An email whitelist is a list of IP addresses from which your users expect to receive legitimate mail. 

When you add an IP address to your email whitelist, mails sent from this IP address will generally not be marked spam. 

To add IP addresses to your email whitelist:

  1. Sign in to your Google Apps administrator control panel.
  2. Select the Settings tab.
  3. Select Email.
  4. Then General Settings once in the Email Settings page
  5. In the Organizations section near the top of the page, highlight your domain.
  6. In the Email whitelist section, enter the IP addresses. (If you would like to add more than one IP address, enter an IP range in CIDR notation or separate each IP address with a comma)
  7. Click Save changes.