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Domains on the Outlook Safe Senders list aren't recognized by Exchange Online or Exchange Online Protection
Content provided by Microsoft
Applies to: Exchange OnlineMicrosoft Exchange Online Protection
Messages that you receive in Exchange Online or Exchange Online Protection are blocked as junk or spam even though you enabled the Never Block Sender's Domain option in Microsoft Outlook.
Currently, safe domains are not recognized by default in Exchange Online or in Exchange Online Protection. Blocked domains, blocked sender addresses, and safe sender addresses are recognized.
Use one of the following methods, as appropriate for your situation:
For stand-alone Exchange Online Protection
For safe sender and blocked sender lists to be respected, directory synchronization must be enabled. By default, safe domains are not synced through directory synchronization. You can modify the configuration to have safe domains synced to Exchange Online and recognized. For more info about how to do this, see Configure content filtering to use safe domain data.