Private Sub Command1_Click()
Dim oMessage As New sevMailActiveX.sevmail
Dim Dateiname As String
Dateiname = App.Path + "\Posteingang\1.txt"
With oMessage
  If .OpenMail(Dateiname) Then
    ' Nachrichten-Parts vorhanden?
    If .Message.MessageCount > 0 Then
      ' Plaintext vorhanden?
      Dim I As Integer
      For I = 0 To .Message.MessageCount - 1
        If .Message.MessageType = "plain" Then
          txtPlain.Text = .Message.Message(I)
        End If
      Next I
 
      ' oder einfacher...
   txtPlain.Text = .TextPlain
 
    End If
  End If
End With
End Sub

   txtPlain.Text = .TextPlain