Document Identification Number (DIN) mandatory for specified CBIC communications; exceptions require written reasons and post facto regularization. Generation and quoting of a Document Identification Number (DIN) is mandatory for specified CBIC communications (search authorizations, summons, arrest memos, inspection notices and inquiry letters) from 8 November 2019; communications without an electronically generated DIN are invalid unless issued under recorded exigent exceptions, which must be regularized within 15 working days by post facto approval, electronic DIN generation and filing. The DIN is system generated, non editable, printable, verifiable by the public on the CBIC website, and requires authorized users to be mapped, credentialed and trained in the DIN utility.