Sent messages disappear after one day in sent folder

Edit Subject

I am new to em CLient and like it very much. However, today I noticed a behavior that is troublesome. I used the program to send 5 -6 emails yesterday after installation. These were saved in the "sent" folder and I saw them this morning. While I was looking at them they disappeared. I don't think I did anything to make this happen. I use that folder to keep a record of emails sent and need to have this be a secure saved mail folder. I checked the settings and the box is clicked to save sent messages in the sent folder. Have you see this behavior before?