Prüfen, ob OL verfügbar ist

Public Class Form1
    Dim timer As New Timer
    Dim olApp As New Microsoft.Office.Interop.Outlook.Application
    Dim items As Microsoft.Office.Interop.Outlook.Items
    Dim isOffline As Boolean

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        With timer
            ' Timer Interval (ms)  
            .Interval = 2000
            ' Eventhandler dem Timer zuweisen  
            AddHandler .Tick, AddressOf timer_tick
            'Timer ist an  
            .Enabled = True
        End With
        'Items zuweisen  
        items = olApp.Session.Stores("user@domain.com").GetDefaultFolder(Microsoft.Office.Interop.Outlook.OlDefaultFolders.olFolderInbox).Items  
        'Eventhandler der Inbox  
        AddHandler items.ItemAdd, AddressOf inbox_itemadd
        'Timer starten  
        timer.Start()
    End Sub

    Private Sub timer_tick(sender As Object, e As System.EventArgs)
        'prüfe ob Session Offline wenn ja setze Variable   
        If olApp.Session.Offline Then
            isOffline = True
        Else    ' Outlook nicht mehr offline  
            If isOffline Then   'wenn Outlook vorher offline war setze erneut den Eventhandler  
                RemoveHandler items.ItemAdd, AddressOf inbox_itemadd
                AddHandler items.ItemAdd, AddressOf inbox_itemadd
                isOffline = False
            End If
        End If
    End Sub

    Private Sub inbox_itemadd(ByVal Item As Object)
        MsgBox("Neue Mail")  
    End Sub
End Class