Modmail

Wiktionary defines modmail as a messaging system on Reddit and similar sites that lets moderators and other users communicate, a compound of "mod" (moderator) and "mail". It cites uses from 2018 to 2023 in books and research papers, such as a 2018 description of it as the internal message tool moderators use to manage their groups. Those are the earliest cited uses, not a documented launch date. Modmail is the channel for appeals and questions about removals, and is separate from ordinary private messages.