We fed this a list of opt-in email addresses from old customers and they mostly all came back clean. Thinking we were safe to send emails to these "valid" email addresses, we sent them, and hundreds bounced back. Turns out that determining whether or not the emails will bounce is not part of their verification process. Looking back through their marketing, it doesn't say that they can detect any invalid email for regardless the reason, but at the same time, it doesn't mention what is an obvious hole in their verification process that led to hundreds of bounce backs. Combined with the fact that they don't offer a refund, warrants 1 "taco".