The 15 Percent Tax on Unverified Lists

Everybody in outbound knows you should verify your email list. Almost nobody knows what skipping it actually costs, because the people who skip it stop measuring around the same time. I measured it, because a campaign of mine paused itself in the middle of a launch and I wanted to know exactly who was to blame.

The setup was ordinary. Four hundred and twenty-two leads, all of them recruitment agency founders in the UK, every address run through a verifier before launch. Three hundred and thirty-three came back good and eighty-nine came back risky. Risky doesn't mean invalid. It usually means a catch-all server that won't confirm either way.

So I sent to all of them, with a bounce guard set to pause the campaign if things went wrong. It paused at 3.76 percent, about three hundred and seventy emails in.

Then I matched every bounce back to the verification result it had been given before launch. Addresses marked good bounced at 0.7 percent. Addresses marked risky bounced at about 15 percent. Twelve of the fourteen bounces came from the risky pile.

Twenty-one percent of the list produced eighty-six percent of the damage.

There's a second lesson in the data. When I later verified a list of four hundred and twenty-four coffee roasters, thirty-eight percent came back as failed to verify. Not bad, just not completed. I re-ran them and seventy-three came back clean. Failed to verify is a timeout, not a verdict.

None of this is clever. It's just the arithmetic nobody publishes, because publishing it means admitting you paused a campaign in front of everybody.

Den Koly runs DenflowAI, routing qualified introductions across recruitment, AI, banking, wealth, specialty coffee and corporate video.