Forum Discussion
Outlook - DesktopApp - Autoreply not working (server not available)
Although Microsoft says the problem has been fixed since version 2508 build 19127.20000 (please see Cannot open the Automatic Replies setting of a shared mailbox in Classic Outlook - Microsoft Suppor...
In that case I'd recommend opening a proper support case directly with Microsoft so that they can obtain logs and traces to analyze why this is still happening in your environment.