For i = 1 To 2

ThisWorkbook.Sheets("Resumen").Range("F5").Value = i
ActiveWorkbook.EnvelopeVisible = True

With ActiveSheet.MailEnvelope

   .Item.To = ThisWorkbook.Sheets("Resumen").Range("B6").Value
   .Item.Subject = ThisWorkbook.Sheets("Resumen").Range("B5").Value
   .Attachment.Add ThisWorkbook.Sheets("Resumen").Range("B7").Value 'THIS LINE SHOW THE MISTAKE, "the object does not admit the method
   .Introduction = "RESUME"
   .Item.Send

End With

ActiveWorkbook.EnvelopeVisible = False
Next i

End Sub