Hi Robin,

i already answerd you at www.outlookcode.com
just for the newsgroup, here is my sample code to do it.

namespace TestAddIn
{
using System;
using Off = Microsoft.Office.Core;
using Ol = Microsoft.Office.Interop.Outlook ;
using Extensibility;
using System.Runtime.InteropServices;
using System.Data;
using System.Xml;
using System.IO;
using System.Reflection;
using System.Diagnostics ;

#region Read me for Add-in installation and setup information.
// When run, the Add-in wizard prepared the registry for the Add-in.
// At a later time, if the Add-in becomes unavailable for reasons such as:
//   1) You moved this project to a computer other than which is was
originally created on.
//   2) You chose 'Yes' when presented with a message asking if you wish to
remove the Add-in.
//   3) Registry corruption.
// you will need to re-register the Add-in by building the MyAddin21Setup
project
// by right clicking the project in the Solution Explorer, then choosing
install.
#endregion

/// <summary>
///   The object for implementing an Add-in.
/// </summary>
/// <seealso class='IDTExtensibility2' />
[GuidAttribute("CFC4FD8C-6769-46C2-8B32-F3ACA3A14CF1"),
ProgId("TestAddIn.Connect")]
public class Connect : Object, Extensibility.IDTExtensibility2
{

 // The Instance Object
 private object myInstance;

 // The Application Object
 private Ol.Application myApplication;

 // The Sent Folder
 private Ol.MAPIFolder mySentFolder;

 // My DataSet
 private DataSet myDataSet;

 // My DataTable
 private DataTable myDataTable;

 /// <summary>
 ///  Implements the constructor for the Add-in object.
 ///  Place your initialization code within this method.
 /// </summary>
 public Connect()
 {
 }

 /// <summary>
 ///      Implements the OnConnection method of the IDTExtensibility2
interface.
 ///      Receives notification that the Add-in is being loaded.
 /// </summary>
 /// <param term='application'>
 ///      Root object of the host application.
 /// </param>
 /// <param term='connectMode'>
 ///      Describes how the Add-in is being loaded.
 /// </param>
 /// <param term='addInInst'>
 ///      Object representing this Add-in.
 /// </param>
 /// <seealso class='IDTExtensibility2' />
 public void OnConnection(object application, Extensibility.ext_ConnectMode
connectMode, object addInInst, ref System.Array custom)
 {
  try
  {
   myApplication = (Ol.Application) application;
   myInstance = addInInst;

   LoadXMLData();
   mySentFolder = myApplication.Session.GetDefaultFolder
(Ol.OlDefaultFolders.olFolderSentMail );
   mySentFolder.Items.ItemAdd +=new
Microsoft.Office.Interop.Outlook.ItemsEvents_ItemAddEventHandler(Items_ItemAdd);
  }
  catch (System.Exception ex)
  {
   Debug.WriteLine(ex.Message);
  }
 }

 /// <summary>
 ///     Implements the OnDisconnection method of the IDTExtensibility2
interface.
 ///     Receives notification that the Add-in is being unloaded.
 /// </summary>
 /// <param term='disconnectMode'>
 ///      Describes how the Add-in is being unloaded.
 /// </param>
 /// <param term='custom'>
 ///      Array of parameters that are host application specific.
 /// </param>
 /// <seealso class='IDTExtensibility2' />
 public void OnDisconnection(Extensibility.ext_DisconnectMode
disconnectMode, ref System.Array custom)
 {
  myInstance = null;
  if (mySentFolder != null)
  {
   // DeRegister Event
   mySentFolder.Items.ItemAdd -=new
Microsoft.Office.Interop.Outlook.ItemsEvents_ItemAddEventHandler(Items_ItemAdd);
   Marshal.ReleaseComObject(myApplication);
  }
  if (myApplication != null)
  {
   Marshal.ReleaseComObject(myApplication);
  }
  GC.Collect ();
 }

 /// <summary>
 ///      Implements the OnAddInsUpdate method of the IDTExtensibility2
interface.
 ///      Receives notification that the collection of Add-ins has changed.
 /// </summary>
 /// <param term='custom'>
 ///      Array of parameters that are host application specific.
 /// </param>
 /// <seealso class='IDTExtensibility2' />
 public void OnAddInsUpdate(ref System.Array custom)
 {
 }

 /// <summary>
 ///      Implements the OnStartupComplete method of the IDTExtensibility2
interface.
 ///      Receives notification that the host application has completed
loading.
 /// </summary>
 /// <param term='custom'>
 ///      Array of parameters that are host application specific.
 /// </param>
 /// <seealso class='IDTExtensibility2' />
 public void OnStartupComplete(ref System.Array custom)
 {
 }

 /// <summary>
 ///      Implements the OnBeginShutdown method of the IDTExtensibility2
interface.
 ///      Receives notification that the host application is being
unloaded.
 /// </summary>
 /// <param term='custom'>
 ///      Array of parameters that are host application specific.
 /// </param>
 /// <seealso class='IDTExtensibility2' />
 public void OnBeginShutdown(ref System.Array custom)
 {
 }

 /// <summary>
 /// Loads the Data from XML File
 /// </summary>
 private void LoadXMLData()
 {
  // Create a new DataSet
  myDataSet = new DataSet ("SentData");

  // Check, if File exists
  if (File.Exists (@"C:\mydata.xml"))
  {
   // Yes, read the XML-Data into Dataset
   myDataSet.ReadXml (@"C:\mydata.xml");
   // Get the DataTable

   if (myDataSet.Tables.Count > 0)
   {
    myDataTable = myDataSet.Tables [0];
   }
  }

  if (myDataTable == null)
  {

   // Create a new DataTable
   myDataTable = new DataTable("DataTable");

   // Add Columns to DataTable (would be nicer with a SchemaFile)
   myDataTable.Columns.Add ("EntryID",Type.GetType ("System.String"));
   myDataTable.Columns.Add ("Subject",Type.GetType("System.String"));
   myDataTable.Columns.Add ("SentOn",Type.GetType("System.DateTime"));

   myDataSet.Tables.Add (myDataTable);

   SaveXMLData();

  }

 }

 /// <summary>
 /// Saves the Data to XML
 /// </summary>
 private void SaveXMLData()
 {
  // Accept Changes
  myDataSet.AcceptChanges ();

  // Save the XML Data
  myDataSet.WriteXml (@"C:\mydata.xml");
 }

 /// <summary>
 /// EventHandler for Items Add Event of Sent Folder
 /// </summary>
 /// <param name="Item">The Outlook Item</param>
 private void Items_ItemAdd(object Item)
 {
  Ol.MailItem myMail = null;
  try
  {
   // Check Item, could be a MeetingRequest also
   if (Item is Ol.MailItem)
   {
    // Cast Object to MailItem
    myMail = (Ol.MailItem) Item;

    // Create a new DataRow
    DataRow newRow = myDataTable.NewRow ();

    // Fill Data into Row
    newRow["EntryID"] = myMail.EntryID;
    newRow["Subject"] = myMail.Subject ;
    newRow["SentOn"] = myMail.SentOn ;

    // Add Row to DataTable
    myDataTable.Rows.Add (newRow);
    myDataTable.AcceptChanges ();

    // Save new Data
    SaveXMLData();
   }
  }
  catch (System.Exception ex)
  {
   Debug.WriteLine(ex.Message );
  }
  finally
  {
   // Release the Reference to MailObject
   if (myMail != null) { Marshal.ReleaseComObject (myMail); }
  }
 }
}
}

Greets, Helmut Obertanner