List Detective: Free Email List Checker

What is List Detective: Free Email List Checker?

Uncover hidden problems in your email list — instantly and for free. Up to 100,000 addresses — runs entirely in your browser, nothing is sent to a server. Built for email marketers who care about deliverability and sender reputation. Try now with the sample data available on the site.

From the website

ListDetective.com: Free Browser-Based Email List Checker

Check your email list before it damages your deliverability and sender reputation. Free, instant, private — your list is processed locally and never sent to a server.