Running MaxBulk Mailer v8.3.4 (Windows 7 PC)

I am sending out a mailout to clients spread over a few days. When I close MBM I save my lists which have the recipients that have already been posted 'marked as sent'.

When I reopen the message the following day, the list is no longer attached & I have to select it from the menu. On opening, the 'marked as sent' data is lost but the recipients sent are all checked. Is there a way of retaining the data & is there a way of marking as sent, all recipients that are checked? It is a long list & would take hours to do manually.