Bad e mail addresses are sometimes marked as valid

Question: We tested Verifier on a set of dummy emails, one that we made up knowing they are fake, using both the Yahoo domain and our own proprietary domains for the fake emails. Only one out of five bad email addresses was flagged as bad and the others were confirmed as valid, looks valid, timeout and "scanning". Your software should have identified all five as bad. We ran another similar test on a larger list of 10 emails, half were true email and half were fake. The software flagged ALL of them as valid.

Answer: For some addresses, such as AOL, Yahoo, and other non-SMTP mail, you can't verify whether the address is good or not. You won't know definitively until some bounce. The mail server won't cooperate and as a result addresses will be marked as valid. In fact, a few ISP's mail servers are configured in a way they prevent anybody to find out if an e-mail address is good or not sometimes to protect their customer e-mail addresses from harvester tools. You can get more information about this here: Bad e-mail addresses are sometimes marked as valid.