FAQ

Email Verification FAQ: Your Questions About MailBounce, Answered

MailBounce combines several signals to give you the most confident verdict possible: syntax checks, MX record lookups over DNS-over-HTTPS, disposable- and role-account detection, free-provider flags, and a live SMTP mailbox check using a real RCPT TO conversation with the receiving server. For most mailboxes this produces a clear valid or invalid result. That said, no email verifier on earth can be 100% accurate in every case, because the final word always belongs to the recipient's mail server. Some providers deliberately accept-all (catch-all domains), some greylist or rate-limit connections, and some intentionally obscure whether a mailbox exists to fight spammers. When we genuinely can't be sure, we tell you so by returning an "unknown" or "catch-all" result rather than guessing — and an "unknown" never costs you a credit.

A catch-all domain is configured to accept mail for any address at that domain — [email protected] and [email protected] will both be accepted at the SMTP layer, even if the second mailbox doesn't actually exist. This is common on corporate domains. Because the server accepts everything, no verifier can definitively confirm whether a specific mailbox is real without actually sending a message. MailBounce detects this condition and labels the address as "catch-all" instead of falsely reporting it as valid. You then decide how to treat catch-alls for your use case — some teams mail them with caution, others exclude them.

Our billing is built around a simple principle: you only pay when we give you a definitive answer. A credit is consumed when a verification returns a conclusive verdict — for example a clear valid or invalid result — and that's one credit per address each time you validate it, on every request or list. You are NOT charged for "unknown" results, because if we can't determine the outcome, it isn't fair to bill you for it. Every account also gets 100 free credits every month. The free validation playground doesn't use credits at all.

Bulk validation lets you upload a list as CSV, TXT, or a ZIP archive, and MailBounce processes it in the background so you don't have to keep a browser tab open. As the job runs, results are sorted into clear categories — valid, invalid, catch-all, unknown, and disposable — and when it's finished you can export the categorized results as a CSV. Processing time scales with list size and with how responsive the recipient mail servers are. For specific per-file size or row limits on your plan, check your dashboard at app.mailbounce.co, since those are tied to your account.

The addresses you submit are used to perform the verification you asked for and to power features that directly benefit you, such as caching results so repeat checks return fast. We treat uploaded lists as your data, not as a resource to resell — we don't sell your contact lists to third parties. To verify a mailbox via SMTP, MailBounce necessarily connects to the recipient's mail server, which is inherent to how email verification works. MailBounce is a newer, smaller service, so rather than claim specific compliance certifications we don't yet hold, we encourage you to review our current privacy terms in-app and reach out with any specific data-handling questions before uploading sensitive lists.

MailBounce is built developer-first. The real-time validation API lives at api.mailbounce.co and returns clean, predictable JSON — including the syntax check, MX status, disposable and role-account flags, free-provider flag, a typo/did-you-mean suggestion, and the SMTP mailbox result. Because each signal is broken out in the response, you can apply your own logic — for example accepting role accounts but rejecting disposables at signup, or surfacing the did-you-mean suggestion inline on your form. Start in the free playground at app.mailbounce.co to see live responses without writing integration code or spending credits.

The playground is a no-commitment way to try MailBounce before you build anything or spend a cent. You can run real validations and see the full, structured result — syntax, MX, disposable/role/free flags, did-you-mean suggestions, and the SMTP outcome — without consuming any credits. It's the fastest way to sanity-check our accuracy on addresses you already know and understand exactly what the JSON looks like before you integrate. No credit card or credit balance is required.

Live SMTP verification checks whether a specific mailbox exists without ever sending an actual email. MailBounce looks up the domain's MX records (via DNS-over-HTTPS), connects to the receiving mail server, and begins the early steps of an SMTP conversation up to the RCPT TO command — essentially asking the server, "would you accept mail for this address?" The server's response tells us whether the mailbox appears to exist, all before any message body is transmitted. The catch is that the recipient server has the final say: catch-all domains will accept every address, and some servers greylist, rate-limit, or deliberately give ambiguous answers. In those cases we return "catch-all" or "unknown" rather than guessing — and you aren't charged a credit for an "unknown."

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