If a requirement can be specified it can be sized, and sizing happens first. Fields are filled only where a source supports them. The file is built to be used, not to be impressive.
Syntax screening
Removing malformed and obviously generated addresses before anything is paid to check them.
Count reconciliation after build
Re-running the figure against the finished extract, so the two cannot drift apart unnoticed.
Contact precedence
Choosing which person represents an organisation when several qualify, by a stated rule.
We will tell you the ceiling before you commit to anything beneath it.