Note: If you want to send response to the sender every time instead of just once, you can apply mailbox server side rule "have server reply using a specific message" to send automatic reply instead of using the OOF rule. This server-side rule will send reply to the sender every time a message is received.

Be careful with this. If two internal users both configure a server-side rule to reply using a specific message it can cause a mail loop. That's why OOFs are better.