Private Declare Function NetMessageBufferSend Lib _
  "NETAPI32.DLL" (yServer As Any, yToName As Byte, _
  yFromName As Any, yMsg As Byte, ByVal lSize As Long) As Long
Private Const NERR_Success As Long = 0&
Public Function SendMessage(RcptToUser As String, _
   FromUser As String, BodyMessage As String) As Boolean

   Dim RcptTo() As Byte
   Dim From() As Byte
   Dim Body() As Byte

   RcptTo = RcptToUser & vbNullChar
   From = FromUser & vbNullChar
   Body = BodyMessage & vbNullChar

   If NetMessageBufferSend(ByVal 0&, RcptTo(0), ByVal 0&, _
        Body(0), UBound(Body)) = NERR_Success Then
     SendMessage = True
   End If
End Function

Private Sub Form_Load()
    Dim RetVal As Boolean
    RetVal = SendMessage("Utente", "FromUser", "BodyText")
End Sub