Email verification — questions answered

Email verification is the process of checking whether an email address is valid, deliverable, and safe to send to. It checks that the address is correctly formatted, that the domain exists and has mail server records (MX), and that the specific mailbox accepts incoming messages. At StopBouncing, we run six checks per address.

The terms are often used interchangeably. Technically, 'email validation' often refers to format/syntax checks (does it look like an email?), while 'email verification' goes further — checking DNS records and performing a live SMTP handshake against the mail server. StopBouncing does both.

Every email service provider — Gmail, Outlook, Mailchimp, SendGrid, Klaviyo — monitors your bounce rate. If too many of your messages bounce (typically above 2%), your account can be throttled, suspended, or blacklisted. Verifying your list before sending protects your sender reputation and ensures your emails actually reach inboxes.

A bounce rate is the percentage of sent emails that couldn't be delivered. 'Hard bounces' (permanent failures like invalid addresses) are especially damaging. Email providers treat a high bounce rate as a signal that you're sending to purchased or unclean lists — which triggers spam filters or account suspension. Most providers recommend staying below 2%.

Disposable email addresses are temporary, throw-away accounts from services like Mailinator, Guerrilla Mail, or 10 Minute Mail. They're used to sign up for things without giving a real address. They're almost never active for more than a few hours. StopBouncing detects disposable addresses across thousands of known providers.

A catch-all domain is configured to accept all incoming emails, regardless of whether the specific mailbox exists. For example, anything@example.com would be accepted even if the mailbox 'anything' doesn't exist. This makes it impossible to confirm via SMTP whether a specific address is real. We flag these as 'unknown' — not invalid.

An unknown address is one we cannot definitively confirm as valid or invalid. This typically means: (1) the domain is catch-all, (2) the mail server blocks SMTP verification, or (3) there was a temporary connection issue. We never classify these as invalid — they may be real, deliverable addresses.

Absolutely. If you run a personal newsletter, a blog with a mailing list, or any kind of email list — even 200 subscribers — you benefit from a clean list. One credit is charged per email checked — regardless of outcome. You only pay for what you use. The minimum pack starts at €10 for 10,000 checks — plus 100 free verifications on signup.

All processing happens on EU-based servers. Uploaded files are permanently deleted within 48 hours of job completion. We do not retain, analyse, resell, or access your email data. A Data Processing Agreement (DPA) is available on request for business customers.

We support .csv, .txt, and .xlsx files. We automatically detect which column contains email addresses — no reformatting needed. If your file has no header row, we use the first column. Duplicates are removed before processing begins.

Yes. Every plan includes full API access. Generate an API key from your dashboard and include it as a bearer token. One API call returns a result in under 2 seconds on average. Ideal for verifying addresses at signup, before they enter your CRM or mailing list.

Yes. One credit is charged for every email we process — regardless of the result (Valid, Invalid, Unknown, or Disposable). This is standard across the email verification industry: a credit pays for the verification attempt, not for a guaranteed conclusive answer. Some domains (catch-all servers, strict SMTP filters) make it technically impossible to confirm whether a specific mailbox exists — but knowing that is itself useful information. We never charge twice for the same email in a single job.

No. Credits purchased via any pack remain in your account indefinitely. There are no monthly fees and no renewal costs.