There is no option to send Out Of Office messages to external (outside the organisation) senders only. You can get this to work using a Rule:

  1. Open Outlook. Click on New Email and create a message you would like to send as an Out of Office, then click File > Save As.

  2. In the opening Save As dialog box, type a name for the new email in the File name box, select the Outlook Template (*.oft) from the Save as type drop down list, and click the Save button

  3. Close the email. Select FileRules and Alerts

  4. Click on New Rule...

    1. Click Apply rule on messages I receive and then click Next

    2. No conditions are needed, click Next again. A warning dialog will check that you meant to apply this rule to all message, click Yes

    3. Click Reply using a specific template under action(s) and then click on Specific template under Step 2

    4. Select the User Templates in File System from the Look In drop down list, select Browse to find the Out Of Office message you created and saved above – once selected click Open

    5. Click Next to continue

    6. Check the Except with specific words in the sender’s address option, and click Specific words under Step 2 – enter the domain of your company (e.g. in the first box, click Add and then OK

    7. Click Next to continue

    8. Name your new rule, check Turn on this rule, review its settings/workflow, and click Finish when done

    <aside> ✉️ Please note that you must do the following in your full Outlook email application so that all these options are available. Outlook on the web (OWA) does not support this as it does not have all the options.