Office 365 provides protection for your email account with automatic filters that divert suspected spam to a separate folder away from the Inbox. While this safeguard is usually helpful, valid emails from companies, colleagues and loved ones may also end up in the spam folder. Creating a whitelist tells the program which domains it should always allow through and eliminates the possibility of missing legitimate emails. You must log in to Office 365 as an Admin to add domains to the whitelist.
To whitelist a domain in Office 365
1. Click the Admin drop-down box at the top of the screen, select Exchange and click the Mail Flow heading.
2. Click the plus sign icon and select Bypass spam filtering from the menu.
3. Type a name for the rule in the appropriate text box. Something simple such as "Whitelist” suffices.
4. Select The senders domain is… from the Apply this rule if drop-down box.
5. Enter the domain you want to allow access. Do not include the entire email address; rather, just include the domain from which it originates, such as “gmail.com.” Click OK when you’re done.