Step 1. Creat a windows form project Message
Step 2. Create form with the following values
             rdoAllUsers - "All Currently Logged in users" - radio button
             rdoCertainUser - "Certain user:" - radio button
            txtUser - textbox for user information
Delay
             rdoNoDelay - "Without delay (until user confirms 'OK') - radio button
             rdoSendWithDelay - radio button
            UD1 - up down control with inital value of 60.
Destination 
            rdoSendToAll - radio button
           rdoSendToSingle - radio button
          lstComputers - listbox
Message
txtMessage - text box multiline max length 125.
lblClearMEssage - clears message
lblCharLeft - number of characters left

btnAbout - Button
btnExit - Exit application
btnSend- Send message button

statusStrip1
-add label to status strip - toolStripStatusLabel1

code for frmMain.cs

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;using System.DirectoryServices;using System.IO;using System.Diagnostics;




namespace Message{    public partial class frmMain : Form    {        public frmMain()        {            InitializeComponent();            toolStripStatusLabel1.Text = "";            rdoNoDelay.Checked = true;            rdoAllUsers.Checked = true;            rdoSendToAll.Checked = true;        }                   private void frmMain_Load(object sender, EventArgs e)        {            DirectoryEntry entry = new DirectoryEntry("LDAP://dc=domain,dc=local");            DirectorySearcher mySearcher = new DirectorySearcher(entry);            mySearcher.Filter = ("(objectClass=computer)");            mySearcher.SizeLimit = int.MaxValue;            mySearcher.PageSize = int.MaxValue;                       foreach (SearchResult resEnt in mySearcher.FindAll())            {                string ComputerName = resEnt.GetDirectoryEntry().Name;                if (ComputerName.StartsWith("CN="))                ComputerName = ComputerName.Remove(0, "CN=".Length);                lstComputers.Items.Add(ComputerName);            }            lstComputers.Sorted = true;            mySearcher.Dispose();            entry.Dispose();        }     
        private void lstComputers_SelectedIndexChanged(object sender, EventArgs e)        {            toolStripStatusLabel1.Text = "Sending messages to: " + " " + lstComputers.SelectedItem.ToString();        }
                private void btnExit_Click(object sender, EventArgs e)        {            Application.Exit();        }
        private void btnSend_Click(object sender, EventArgs e)        {            String msgStr = "ds";            string sndTo;            decimal sendTime;            string sndToComp;                if(txtMessage.Text.Length < 1)            {                MessageBox.Show("Must Enter a Message to send!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);                txtMessage.Focus();                return;            }                    if (ClsMsg.SendToAllUsers)            {                sndTo = "*";            }            else            {              if (txtUser.Text.Length > 1)                {                    sndTo = txtUser.Text;                }              else                {                    MessageBox.Show("Enter Value for user to send to");                    txtUser.Focus();                    return;                                   }            }                        if (ClsMsg.SendWithDelay)            {                sendTime = UD1.Value;            }           else            {                sendTime = 0;            }
            if (ClsMsg.SendToAll)            {                sndToComp = "*";            }            else            {                sndToComp = lstComputers.SelectedItem.ToString();            }
            if (LocateMsgExe(out string strMsgPath))            {                const string quote = "\"";                string msg = quote + txtMessage.Text + quote;                msgStr = sndTo +" " + " /Server:" + sndToComp + " " + "/Time:"  + sendTime + " " + msg;                                Process.Start(strMsgPath, msgStr);                  toolStripStatusLabel1.Text = "Message sent to " + sndToComp + " At " + DateTime.Now;                                           }        }
        public static bool LocateMsgExe(out string returnedMsgPath)        {            returnedMsgPath = null;            string[] msgPaths = new string[] { Environment.ExpandEnvironmentVariables(@"%windir%\system32\msg.exe"),                                     Environment.ExpandEnvironmentVariables(@"%windir%\sysnative\msg.exe") };
            foreach (string msgPath in msgPaths)            {                if (File.Exists(msgPath))                {                    returnedMsgPath = msgPath;                    return true;                }            }
            return false;        }
        private void rdoAllUsers_CheckedChanged(object sender, EventArgs e)        {            txtUser.Text = "";            txtUser.Enabled = false;            ClsMsg.SendToAllUsers = true;
        }
        private void rdoCertainUser_CheckedChanged(object sender, EventArgs e)        {            txtUser.Enabled = true;            ClsMsg.SendToAllUsers = false;                  }
        private void rdoNoDelay_CheckedChanged(object sender, EventArgs e)        {            UD1.Enabled = false;            ClsMsg.SendWithDelay = false;        }
        private void rdoSendWithDelay_CheckedChanged(object sender, EventArgs e)        {            UD1.Enabled = true;            ClsMsg.SendWithDelay = true;
        }
        private void UD1_ValueChanged(object sender, EventArgs e)        {            ClsMsg.DelayTime = UD1.Value;                 }
        private void rdoSendToAll_CheckedChanged(object sender, EventArgs e)        {            lstComputers.Enabled = false;            ClsMsg.SendToAll = true;
        }
        private void rdoSendToSingle_CheckedChanged(object sender, EventArgs e)        {            ClsMsg.SendToAll = false;            lstComputers.Enabled = true;                    }
        private void lblClearMessage_Click(object sender, EventArgs e)        {            txtMessage.Text = "";
        }
        private void txtMessage_TextChanged(object sender, EventArgs e)        {            lblCharLeft.Text = 125 - txtMessage.Text.Length + " Characters Left";
        }
    
        private void btnAbout_Click(object sender, EventArgs e)        {            MessageBox.Show("Created By Mandy");        }    }}

And create a Class named clsMsg

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;
namespace Message{    public static class ClsMsg    {        public static bool SendToAllUsers { get; set; }        public static decimal DelayTime { get; set; }        public static bool SendWithDelay { get; set; }        public static bool SendToAll { get; set; }        public static bool SendToOne { get; set; }        public static string ComputerName { get; set; }

    }}
Message Center
