jcoffey-dev is traveling from Thursday 1 October through Sunday 4 October. Issues and pull requests are welcome, and will get an answer after that. Thanks for your patience.
All six settled as recommended. Answer 6 ("and any other recognized and protected PII") becomes a catalog of identifiers with published formats and checks, grouped by region, each either checked by its check digit or counted only beside a corroborating word, plus templates named for what they find. Data with no number to find is covered by word lists and not claimed as detection. Office documents are read; PDF counts as can't be inspected.
Phase 1: one native rule engine at DATA, after the system Sieve script,
for both DLP policies and transport rules. DLP checks outgoing mail
with counted detectors (payment cards, IBAN, US SSN, word lists,
patterns) and blocks, warns with an audited override, or holds for
review. Held mail stays in the queue unscheduled, with its own review
record, so the queue's stored format is unchanged. Matches go to the
audit log without the matched text. Six questions for John at the end.