Hello @Rising Flight ,
From your description, what you're saying is that you need to create a rule that assigns an action to any email from the external email [abc@extdomain.com] that has the words "at abc" in the subject? If so, you could try creating a rule by following these steps:
1.Open Outlook, click the "Rules" drop-down list in the "Home" tab, click "Manage Rules and Alerts", and then click "New Rule".
2.In the Rules Wizard, select "Apply rules on messages I receive" and start from a blank rule. Click "Next". Select the condition "with specific words in the subject’" and click on the underlined word "specific words" in the bottom box. In the Search Text dialog box, enter "at abc" and click Add. Click OK when finished. Select the criteria "From People or Public Group" and click on the underlined "People or Public Group" in the bottom box. In the "Rule Address" dialog box, type [abc@extdomain.com] at "from ->" and click "OK" when completed.
3.Click Next and select the action you want to apply to eligible messages. For example, you can choose to move them to a specific folder, mark them for follow-up, or delete them.
4.Click Next and select any exceptions you want to apply to the rule. For example, you can exclude messages marked as important or that contain attachments.
5.Click Next and give the rule a name. You can also choose whether to run the rule on messages already in your inbox or only on new messages. Click Finish and then OK to save the rule.
Through the above steps, you should be able to get the expected results. If you have any other questions, please feel free to contact us.
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