source: binary-improvements/7dtd-server-fixes/src/CustomCommands/Reply.cs@ 143

using System;
using System.Collections.Generic;

namespace AllocsFixes.CustomCommands
{
        public class Reply : ConsoleCommand
        {
                public Reply (ConsoleSdtd cons) : base(cons)
                {
                }

                public override string Description ()
                {
                        return "send a message to  the player who last sent you a PM";
                }

                public override string[] Names ()
                {
                        return new string[] { "reply", "re" };
                }

                private void SendMessage (ClientInfo _receiver, ClientInfo _sender, string _message)
                {
                        PrivateMassageConnections.SetLastPMSender (_sender, _receiver);
                        string senderName = CommonMappingFunctions.GetPlayerName (_sender);

                        CommonMappingFunctions.GetConnectionManager ().networkView.RPC ("RPC_ChatMessage", _receiver.networkPlayer,
                                new object[] {
                        _message,
                        -1,
                        senderName + " (PM)",
                        true
                }
                        );
                        string receiverName = CommonMappingFunctions.GetPlayerName (_receiver);
                        m_Console.SendResult ("Message to player " + (receiverName != null ? "\"" + receiverName + "\"" : "unknownName") + " sent with sender \"" + senderName + "\"");
                }

                private void RunInternal (ClientInfo _sender, string[] _params)
                {
                        if (_params.Length < 1) {
                                m_Console.SendResult ("Usage: reply <message>");
                                return;
                        }

                        string message = _params [0];
                        for (int i = 1; i < _params.Length; i++) {
                                message += " " + _params [i];
                        }

                        ClientInfo receiver = PrivateMassageConnections.GetLastPMSenderForPlayer (_sender);
                        if (receiver != null && CommonMappingFunctions.GetClientID (receiver) >= 0) {
                                SendMessage (receiver, _sender, message);
                        } else {
                                if (receiver != null) {
                                        m_Console.SendResult ("The sender of the PM you last received is currently not online.");
                                } else {
                                        m_Console.SendResult ("You have not received a PM so far.");
                                }
                        }
                }

                public override void ExecuteRemote (string _sender, string[] _params)
                {
                        try {
                                m_Console.SendResult (string.Format ("{0} executing remote command '{1}' {2}", _sender, this.Names () [0], string.Join (" ", _params)));
                                ClientInfo ci = CommonMappingFunctions.GetClientInfoFromSteamID (_sender);
                                RunInternal (ci, _params);
                        } catch (Exception e) {
                                Log.Out ("Error in Reply.ExecuteRemote: " + e);
                        }
                }

                public override void Run (string[] _params)
                {
                        Log.Out ("Command \"reply\" can only be used on clients!");
                }
        }
}