Cached Exchange Mode is basically the option to locally store only the past week, month, etc. of messages and attachments. Outlook for Windows has had this feature since Office 2007. Outlook for Mac 15.6, released last week, still lacks this feature. And I know of no other Exchange-capable email client for OS X that has this capability. Oddly enough, Apple's iOS mail client is capable of doing what OS X mail couldn't. If anyone knows of an OS X mail client with this feature, it would be much appreciated. Thanks.