http://www.rfc-editor.org/rfc/rfc3888.txt
RFC 3888: Message Tracking Model and Requirements, T. Hansen2004-09-01T23:00:00-00:00Customers buying enterprise message systems often ask: Can I track the messages? Message tracking is the ability to find out the path that a particular message has taken through a messaging system and the current routing status of that message. This document provides a model of message tracking that can be used for understanding the Internet-wide message infrastructure and to further enhance those capabilities to include message tracking, as well as requirements for proposed message tracking solutions. This memo provides information for the Internet community.