Abstract: The invention provides a system and method for the automatic detection of items as originating from a specific source, e.g. client or customer, identifying specific characteristics of the items, comparing these characteristics to a database of sets of such characteristics identified with or more sources, and providing an output of items that match the characteristics. In one embodiment of the invention, a mailer detection and manifest system detects mail pieces that were sent by specific mailers using mail piece characteristics that are unique to the mail pieces of each mailers' job within a mixed mailer mail stream. This is preferably accomplished in real-time or near real-time while sorting the mail pieces after the mailers' specific mail piece characteristics have been determined.