Symptoms
In Microsoft Outlook, some mailbox rules seems to be out of order. Also, you find that the rule priority has changed unexpectedly when you examine it on the Exchange mailbox server by using the following Windows PowerShell command:
Get-InboxRule -Mailbox identity After you correct the rule priority, this behavior may recur.
Cause
This behavior may occur in the following scenario:
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Many rules are created in Microsoft Outlook.
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Additional rules are created or changed in Outlook Web App (OWA).
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The rules are viewed in the Outlook Rules and Alerts field on the File tab.
Note The rules don't have to be changed to cause this behavior.
Resolution
This behavior occurs if changes to rules are regularly made in both OWA and Outlook. If changes to the rule order or priority affect the desired functionality of the rules that are used, we recommend that you create and manage rules exclusively in either OWA or Outlook, but not both.
Notice that some rule options are available in OWA only. If these options are required, and if the rule priority must be maintained, rules should be edited or viewed only through OWA instead of through Outlook. Opening the Rules and Alerts dialog in Outlook can cause a reorder of the rules, even if no changes are made.