Outlook 2010 用代码在Outlook explorer中选中一个邮件

这个代码只能在Outlook 2010中使用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Office.Tools.Ribbon;
using Outlook = Microsoft.Office.Interop.Outlook;
using System.Windows.Forms;
namespace OutlookAddIn18
{
    public partial class Ribbon1
    {
        private void Ribbon1_Load(object sender, RibbonUIEventArgs e)
        {

        }

        private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            Outlook.Application app = Globals.ThisAddIn.Application;
            Outlook.Explorer exp = app.ActiveExplorer();
            Outlook.MailItem item = app.Session.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox).Items[3];
            exp.ClearSelection();
            exp.AddToSelection(item);
        }
    }
}