Nathan P.

run them through million verifier is best in class and cheapest 1m credits is like £400, 25k is £25

I use sendpilot/ heyreach, they have native integrations with clay, sendpilot is cheaper and has a lifetime plan on appsumo, heyreach is best in class even can use something like dripify. I use sendpilot in my business though and is probably my recommendation