A system and method applied to a communications network which transmits document portions in which an original document portion having an identifier portion and an information portion is replaced or swapped with a substitute null document portion. The reads the identifier portion of the original document portion, determines the information portion of the original document portion, and issue a swap order when an undesired original document portion is found. A modified document is created by inserting the substitute null document portion in place of the undesired portion and the modified document is passed on to the user set and displayed. Also, the system performs detection and replacement of undesired content in emails, such as junk mail, viruses and confidential material.