What email verification actually tells you (and what it doesn't)

Most people run an email list through a verifier, see a column of green and red, and treat it as a delete-or-send decision. That works right up until it doesn't — because two of the most common verdicts aren't green or red at all, and what you do with those is what actually decides whether your campaign lands.

Here's what each verdict means, what it's worth trusting, and where the real judgment calls are.

How verification works at all

Nobody looks up whether an email exists. There's no directory. Verification is a sequence of narrowing checks:

• Syntax — is this even a well-formed address? Catches typos and junk instantly, costs nothing.
• Domain and MX records — does the domain exist, and does it have a mail server? A domain with no MX record cannot receive email, full stop.
• Known-bad lists — is this a disposable domain, the kind people use to grab a lead magnet without giving you a real address?
• Mailbox probe — a conversation with the receiving mail server that asks, without sending anything, whether it would accept mail for this specific address.

That last step is where it gets interesting, because the answer isn't always yes or no.

The verdicts

Valid — the mail server confirmed it would accept mail for this address. This is the one you can act on with confidence. Send.

Invalid — the server rejected it. The mailbox doesn't exist, or it's been closed. Sending here is how you earn bounces, and bounces are what wreck sender reputation. Remove it.

No mail server — the domain has no MX record at all. Often a parked domain, a typo of a real company, or a business that folded. Nothing can arrive. Remove it.

Malformed — it failed the syntax check. A missing @, a stray space, a .con where you meant .com. Worth eyeballing these; some are recoverable by hand if the intent is obvious.

Disposable — a throwaway domain. The address probably worked for exactly as long as it took someone to confirm a signup. Technically deliverable, practically worthless. Remove it, and consider blocking these at your signup form instead of cleaning them up later.

Role address — info@, sales@, support@, hello@. These are real and deliverable, but they're shared inboxes, often monitored by several people or none. Reply rates are poor and spam filters treat them with more suspicion. Not junk, but not a person either. Segment them; don't put them in a one-to-one sequence.

Catch-all — this is the one that trips people up. Some domains accept mail for any address at that domain, so real.person@company.com and absolute.nonsense@company.com both get a yes. The server's acceptance tells you nothing about whether that specific mailbox exists.

Unknown — the server didn't answer, timed out, or gave a response nobody can interpret. This isn't a verdict about the address; it's a verdict about the attempt. Try again later.

What to actually do with catch-alls

Catch-all is a judgment call, and the honest answer is that it depends what you're sending.

You can't prove the mailbox exists, so you're weighing risk. If the address came from a reliable source — a form fill, a business card, an enrichment tool that found it via a verified pattern — a catch-all domain is usually fine to send to. If it came from a guessed pattern like firstname.lastname@ with nothing corroborating it, you're gambling.

The practical approach: send to catch-alls, but keep them in their own segment, so a bounce spike is visible immediately rather than buried in your main list's numbers. Warm domains handle a few catch-all bounces fine. A cold domain sending its first campaign into a pile of unverifiable addresses does not.

Roughly one in five B2B domains is catch-all. Deleting them all is expensive; sending to them blindly is risky. Segmenting costs you nothing.

The numbers that matter after you verify

Once your list is clean, two figures tell you whether you're in good shape.

Keep your bounce rate under 2%. Above that, mailbox providers start treating you as someone who doesn't maintain a list. Above 5% and you're in genuine trouble — it's the fastest way to land in spam folders for every recipient, not just the bad addresses.

Watch how long it's been since you verified. B2B email decays at roughly 2–3% per month as people change jobs. A list verified six months ago is meaningfully worse than one verified last week, even if nothing about it looks different. Re-verify before any large send.

What verification cannot do

Verification tells you an address can receive mail. It does not tell you the person still works there, that they'll open it, or that your message is worth their time. It's a hygiene check, not a targeting strategy. Clean lists don't rescue bad messaging — they just make sure your good messaging arrives.

Try it

You can check any address free with the prospiq email verifier — no signup, 5 checks a day. If you need to do a whole list, a free account gets you 25 verifications a month plus CSV upload for up to 10,000 addresses at a time, with catch-all and role detection labelled on every row.

And if we can't get an answer for an address, that check is free. We'd rather tell you we don't know than sell you a guess.