Type/paste the email addresses in the "input" field (one address for each line)
Press the "check emails" that will appear.
If there are "not accepted" emails, clean the typos untill all the issues are cleared.
The "verified" list now contains all the good emails, that can be copied to a new file.
Use case:
You are asked to send a DeM (Direct e-mail Marketing) to a number of customes, but the marketing department gives you a hand-made XLS file, with typos and duplicates.
They ask you to clean the mess too.
Disclaimer:
E-mail data is never sent to any server, or even stored locally.