starface-outlook-sync-addin/src/StarfaceOutlookSync/Program.cs

using System;
using System.Threading;
using System.Windows.Forms;

namespace StarfaceOutlookSync
{
    static class Program
    {
        private static Mutex _mutex;

        [STAThread]
        static void Main()
        {
            // Nur eine Instanz erlauben
            const string mutexName = "StarfaceOutlookSync_SingleInstance";
            _mutex = new Mutex(true, mutexName, out bool createdNew);

            if (!createdNew)
            {
                MessageBox.Show(
                    "Starface Outlook Sync laeuft bereits.",
                    "Starface Outlook Sync",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Information);
                return;
            }

            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new UI.MainForm());
        }
    }
}