A list where a fifth of the addresses bounce does not just waste a fifth of the sends. It damages the sending reputation that the other four fifths depend on.
The catch-all problem
A large share of company domains accept mail to any address, which means a standard verification returns a pass for a mailbox that does not exist. Treating those passes as clean is the single most common way a list that looks verified still bounces.
So catch-all and unknown results are routed to a second check of a different kind rather than being accepted or rejected wholesale. Accepting them inflates your bounce rate; rejecting them throws away a meaningful part of most B2B markets.
Finding, then verifying again
When the address on file is unusable, several finders are tried in sequence. Every candidate that comes back is put through the same verification rule as the original. This sounds obvious and is routinely skipped, because a freshly found address feels authoritative. It is not.
Stopping early
The sequence stops at the first clean result rather than running every finder and picking. That is a cost decision: the later finders are the expensive ones, and most people are resolved before you reach them.
What it does not do
It never sends anything, including a test message. Verification here is inference from the mail infrastructure, not from contacting the person.
Runs well with
Skills compound. These are the ones we usually install alongside it.