Est run time: 30-60s, depending on number of rows.

Usefulness: Email validation tools are stupidly expensive! So we decided to build our own, using a mixture of proprietary datasets, regex logic, MX DNS checks, and, finally, API integration with some well-known email validation services. It doesn't make sense that we offer this for free, so PLEASE PLEASE BECOME A SPONSOR SO WE CAN FEED OUR CHILDREN.

Caveats: Many domains (especially enterprises) are "catch-all", meaning it's impossible to verify a specific email without, like, being in an email thread with said person. But, for everything else, this verification should be pretty accurate.