Free tool
Email address checker
Bounces are the fastest way to damage a sending domain's reputation, and most of them are avoidable typos and dead domains. Check an address for both.
Limited to 20 addresses a day so it stays a tool rather than a list-cleaning service.
One at a time is not how you clean a list
This checks a single address, 20 a day. Oxeyo runs the same syntax and MX check on every address in a CSV as you import it, flags the ones that look wrong before you send, and suppresses a hard bounce automatically so the same address is never emailed twice.
Import a list and verify it