James Moshides's dashboard

I like to keep emails in the sent folder but I noticed that when I open old sent emails, it is blank and the message is missing. Also, when I open an old sent email which has an attachment symbol, it is blank and when I return out of it the attachment symbol disappears. It it an automatic deletion of old emails? or is a virus wrecking my sent email records? Hope someone can help. Jim, Sydney, Australia