Public category that accepts emails and mention an AI-bot. It should work.
Or using Chatbot, the other AI solution for Discourse, and its auto answering option.
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And by PM that should work too. It may need some group adjustments, but after all an AI bot is (at least) ”just” another TL4 user. But I wouldn’t ever allow that for ordinary users. It is too risky, and could be really costly really fast.