Five-provider email waterfall

1. Normalize inputs — proper-case name, root company domain.
2. Provider 1 (cheapest) on all rows.
3. Provider 2 only where step 2 is empty.
4. Provider 3 (premium) only where domain is set and headcount >= 25.
5. Pattern guess as the final fallback.
6. Validation pass on every result.
7. Write a status column: valid / risky / none.
8. Only rows marked valid flow to your sequencer.

How to use it

1. 1Set a run condition on every provider column so it fires only on empty rows.
2. 2Track cost per valid email weekly and reorder providers by hit rate.