What are some alternatives?
When comparing mails.wtf and Email List Verify, you can also consider the following products
Hunter - Find all the email addresses related to a domain
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
LeadGibbon - Access millions of business contacts, with verified email addresses and phone numbers
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Mail Dump - Powerful Extensions for email addresses extracting, verifying and finding
Email Verifier - Email verifier app lets you verify email.