Document Identification Number requirement: all CBIC communications must carry a verifiable DIN or be treated as invalid. The notice mandates electronic generation and quoting of Document Identification Number (DIN) on all communications (including emails) by any CBIC office, extending prior DIN use on enforcement documents to all correspondence to create a digital audit trail and allow online verification via the Directorate of Data Management portal; communications without an electronically generated DIN, except as previously exempted, will be treated as invalid unless regularised per the stated procedure.