Cached Exchange Mode
If you noticed that you are missing emails while using the Outlook 2013 Desktop Client, your Use Cached Exchange Mode might be set to another value other than All, the default is 12 months. To change this setting please follow this link. The link will guide you through on setting this option. To see all your mail, slide the slider all the way to the right, this value should be ALL.
If you are missing emails on the Outlook Desktop Client, your Use Cached Exchange Mode might be set for an other value other than All.