It is considered a best practice to archive the fax's XML data for auditing purposes and create a cross reference between the fax and its source XML.
In order to cross reference a fax to its fax history, both Document Types must be assigned the Fax Unique ID Keyword Type and this Keyword value must be mapped to populate automatically from the fax handle property (the fax handle is a unique identifier used by the fax server to identify a specific fax).