Hello @Glenn Maxwell,
Welcome to the Microsoft forum for technical support.
Based on your description, it is recommended that you follow the steps below to set up this rule:
- Log in to the Exchange admin center.
- Go to Mail Flow → Rules.
- Click "+" to create a new rule.
- In the new rule form, create the rule as shown in the screenshot below.
Please feel free to contact me if you have any queries.
Best,
Jake Zhang