Hi Agit! This is an interesting suggestion. I moved it to its own topic in the Feature category, where feature requests are considered.
This does sound like an interesting use case. Like you mentioned, we use group inboxes ourselves to provide support, and typically leave them open ended. We don’t close them so the customer can continue to write back to ask followup questions. On our end when we have added a reply, we archive the message so everyone on our team knows it has been answered.
These PMs can get long, so it would be interesting to be able to mark one particular reply as the answer to the question in the first post.