O365: Create White list domain (Allow list) in Exchange online with Mail Flow Rule

Chetta Busayarat

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O365: Create White list domain (Allow list) in Exchange online with Mail Flow Rule
Photo by Le Vu / Unsplash


To create or allow trusted domain on Exchange online by Mail Flow Rule.

  1. Login to microsoft admin portal: admin.exchange.microsoft.com
  2. Goto "Mail Flow" > "Rules" > "Add a rule"

  1. "Create a new rule"

  1. Name and set conditions for the rule as below example

  1. Next

  1. Set rule setting
    1. Rule mode: Enforce
    2. Checked: Stop processing mor rules (Mean: if email matched with this rule then stop check with the next rule)
    3. Match sender address in message: Header (System check domain on header)


7. Review rule before finish

  1. Finish

  1. New rule will show in the list



10 . Don not forget to enable this rule.



Note: Do not allow pubic domain to whitlist (example "gmail.com", "outlook.com") as it will allow all that domain email to your email system.