Email whitelist or blacklist
Email whitelist - An email whitelist is a list of IP addresses that you deem are acceptable for sending mail to your domain and should not be labeled as spam. At this time, this feature is available only in Google Apps for Business or Education. If you notice that legitimate emails from specific contacts are incorrectly marked spam, you can whitelist the contact's IP address. Once you whitelist the IP address, message originating from this IP will no longer be marked spam. Learn more
Email blacklist - An email blacklist is a list of email addresses or IP addresses that you want to block from sending mail to your domain. Administrators can block certain domains or users using the Blocked senders setting. Additionally, each user can create a filter in their individual mailbox to automatically send messages from specific users or email list to Trash. Users can also prompt our spam filters by reporting unwanted messages as spam.