You can find software or apps online that validate email addresses in bulk or individually. There is usually a user fee associated with using these services. On Google, you can find listings of such services. Below, I have included links to two examples of email verification services.

An online website:
https://www.verifyemailaddress.org/#result

This website can validate individual email addresses and email addresses in bulk. To use the bulk email verification, a file containing the email addresses must be uploaded to the web page. Uploaded files to the web page are not saved for any reason.

Email Verification Software:
https://www.downloadcloud.com/email-validation-software.html

A number of downloadable email verification software names are listed. For privacy reasons, these listed software could be better than online email verifiers.