Set up a shared inbox

Team → Shared inboxes → Share another mailbox. Pick the mailbox (Team plan). Then Manage access to choose the members; owners and admins always have access.

Every conversation in a shared inbox has a status (Open, Waiting, Closed) and an owner. Use the Mine / Unassigned / All / Closed tabs above the list, assign from the reader, and leave internal notes with @mentions that the customer never sees.