Hi @Florjan Ajdnik ,
An OOF response is sent one time per recipient, this is by design. If you want to send a response to the sender every time instead of only one time, you can apply the "have server reply using a specific message" mailbox server-side rule instead of using the OOF rule.
- Open Outlook client, select the File > Manage Rules & Alerts.
- In the Rules and Alerts dialog box, on the E-mail Rules tab, click New Rule.
- Under Start from a blank rule, click Apply rule on messages I receive and click Next.
- To reply to every email message you receive, leave the Step 1 and Step 2 boxes unchanged and click Next again. Select Yes when Outlook asks you if you want to apply this rule to all messages.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.