At Fork.ai I sold leads to sales teams, marketers, and agencies over cold email. Before every send I ran the list through whatever verifier we could afford that week. The results failed in both directions. Addresses marked safe still bounced and burned the sending domain. And the invoice was high enough that running a risky list a second time felt stupid — so we didn't. I stopped trusting the 99% accuracy claims. Mailbox providers rate-limit, greylist, and lie to unknown senders. That is how email works. No verifier, including us, can honestly promise 99%+ on every address. So I built BillionVerify to control the part we actually could: cost. It runs at about one-tenth of what we used to pay those vendors. When a check is that cheap, you can verify a doubtful address more than once and raise the hit rate — instead of paying once, hoping the first pass was right, and finding out from a bounce.