source: binary-improvements/AllocsCommands/PrivateMessageConnections.cs@ 331

using System.Collections.Generic;
using Steamworks;

namespace AllocsFixes.CustomCommands {
        public class PrivateMessageConnections {
                private static readonly Dictionary<CSteamID, CSteamID> senderOfLastPM = new Dictionary<CSteamID, CSteamID> ();

                public static void SetLastPMSender (ClientInfo _sender, ClientInfo _receiver) {
                        senderOfLastPM [_receiver.steamId] = _sender.steamId;
                }

                public static ClientInfo GetLastPMSenderForPlayer (ClientInfo _player) {
                        if (!senderOfLastPM.ContainsKey (_player.steamId)) {
                                return null;
                        }

                        CSteamID recSteamId = senderOfLastPM [_player.steamId];
                        ClientInfo recInfo = ConnectionManager.Instance.Clients.ForSteamId (recSteamId);
                        return recInfo;
                }
        }
}