How does LeadIQ verify email addresses?

The way we verify emails is the following:

• We contact their mail server and ask, for example, "Does [e-mail] exist?" and their mail server should say yes since that is valid.  
• Then we ask "Does [e-mail] exist?"  and they should say No because it's not valid.  If it says No, we know it only accepted the legit email and we consider it verified.
• If they say yes to all formats, we can not verify the email because it's using a Catch-All system and accepting all mail and then rejecting it on the backend.  This is an Unverified status.
• If we have a verified email from someone at a company, and other emails are unverified, we assume the company uses the same format for everyone, which isn't always the case (for example, we have 3 Ryans working for us, so they have various versions of emails).  We list those as "Best Guess"

We also do use other methods, including third-party vendors, as data sources beyond our own testing.