Neverbounce and only use the “valid” emails.

Neverbounce performs better according to the data on our cold outreach platform

Hunter.io is my personal favorite

You can use https://leadshield.io. Integrates directly with a bunch of CRMs
easily import your list. FYI I am the owner if you have any questions.

Kickbox or datavalidation - I did a test on 800emails with 12 e-mail validation
tools are those two are the most reliable ones

Kickbox - get 10k credits with code MONKEYBLOCKS

I tested out a bunch a couple of years ago and kickbox gave the most detailed
reports on our lists so I’ve stuck with them ever since

Love Neverbounce https://neverbounce.com/

Snovio.com is my recommendation

Mailifier! Currently available as lifetime deal on Dealify

Kickbox