Environment: Outlook desktop and web apps
Purpose: How to whitelist a sender or domain
Add a sender or domain to the safe senders list
Safe senders are people and domains you always want to receive email messages from. Safe recipients are recipients that you don't want to block, usually groups that you’re a member of. Messages received from any email address or domain in your safe senders and recipients list are never sent to your Junk Email folder.
IMPORTANT: The server that hosts your mailbox may have junk email filtering settings that block messages before they reach your mailbox.
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Sign in to Outlook Web App. For help, see Getting started in Outlook Web App.
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At the top of the page, select Settings 
> Mail.
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Under Options, select Block or allow.
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To add an entry to Safe senders and recipients, enter the email address or domain that you want to mark as safe in the Enter a sender or domain here text box, and then press Enter or select the Add icon 
next to the text box.
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For example, to mark all email from addresses that end in contoso.com as safe, enter contoso.com in the text box.
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To mark a specific person as safe, enter that person's full email address. For example, to mark all messages from KatieJ@contoso.com as safe, enter KatieJ@contoso.com in the text box.
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(Optional) Select the Trust email from my contacts check box to treat email from any address in your contacts folders as safe.
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Select Save to save your changes.