CodeSteps.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Microsoft.Office.Tools.Ribbon;

using Outlook = Microsoft.Office.Interop.Outlook;


namespace CodeSteps_AddIn
{
    public partial class CodeSteps
    {
        private void CodeSteps_Load(object sender, RibbonUIEventArgs e)
        {

        }

        private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            Outlook.Explorer explorer = Globals.ThisAddIn.Application.ActiveExplorer();

            // -- Display folders list
            if (explorer != null)
            {
                String folders = "";


                foreach (Outlook.Folder mailbox in explorer.Session.Folders)
                {
                    folders += mailbox.Name + "\n";

                    try
                    {
                        foreach (Outlook.Folder folder in mailbox.Folders)
                        {
                            folders += "\t" + folder.Name + "\n";
                        }
                    }
                    catch(Exception ex)
                    {
                        ; // nothing to do, for the moment
                    }
                }

                System.Windows.Forms.MessageBox.Show(folders);
            }
        }
    }
}