Attachment execute service (AES) is an attachment security platform enhancement introduced for Windows XP Service Pack 2.  AES provides a framework that allows both Microsoft and external (third party) developers to have the same security services available to them while developing email, IM and other file transfer clients.

MSDN developer information:  (make sure to look at the sample in the SDK)

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/shell/reference/ifaces/iattachmentexecute/iattachmentexecute.asp?frame=true