Hi @Steve,
By research, it is recommended that you can use a shared email account to log in to OWA and set up automatic replies to external emails, such as the settings below.
Please note when the Out of Office Assistant is enabled, only one reply is sent to each sender, even if you receive multiple messages from that person. More information you can refer to: Only one reply is sent to each sender when Out of Office Assistant is enabled - Exchange | Microsoft Learn
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