Sample and verify
Written definitions for every column.
Nothing is sourced until the shape of the audience is settled. Where a rule rejects a row, the reason travels with the rejection. Delivery includes a plain statement of what the file will not do.
Match confidence
Separating confident pairs from probable ones, and reporting the latter rather than folding them in silently.
Catch-all detection
Separating addresses that are confirmed from addresses on a domain that accepts anything.
Sending identity
Separating what you send in volume from how your main domain is treated.