Hi @Federico Coppola ,
“Only one time I got OOF, however I sent more or less ten mails to the same mailbox.”
According to this official documentation: Understand and troubleshoot Out of Office (OOF) replies - Exchange | Microsoft Learn
It mentions that if automatic replies are enabled, only one reply is sent to each sender even if a recipient receives multiple messages from a sender.
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. This alternative rule sends a response every time that a message is received.
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