Email verifier — check if an email address is valid before you send

To check whether an email address is valid, run it through an email verifier: it asks the receiving mail server about that address and reports back whether mail sent there would actually arrive. WarmySender's verifier returns one of four clear results — valid, invalid, risky or unknown — plus catch-all detection, so you know when a domain accepts everything and no single address on it can be confirmed. Do it before you send, not after a bounce has already cost you.

One free check a day costs nothing — paste one address into the verifier and read the result, with no account and no card. For a whole list there are two ways to pay, and you do not need a subscription for either: buy one-time verification credits from $79 for 100,000 (they never expire), or use the monthly allowance that comes included with any WarmySender plan.

One thing to be clear about up front: the verifier checks addresses you already have — it does not produce an address you're missing. If a contact has no address yet, that comes from importing a list that already includes it or saving a contact from the B2B lead database.

WarmySender runs your outreach on autopilot with AI agents, across Cold Email, Email Warmup, LinkedIn, Instagram and Multichannel sequences — so once your list is clean you can warm up your mailboxes and send from the same dashboard. But the verifier stands alone: you can use it and never touch the rest.

How to check an email address

Checking one address takes a few seconds:

1. Paste the address into the email verifier and run the check. No account is needed for your free daily check.
2. Read the result. You get one of four answers — valid, invalid, risky or unknown — and every result also names the precise reason behind it: a shared team address, a full inbox, a switched-off account, an accept-all domain or a throwaway provider, plus a 0–100 confidence score.
3. Act on it. Send to valid. Remove invalid. Treat risky with care. Re-check unknown later.

Checking a whole list works the same way, one pass instead of one address: upload your list (or pick a list you already have in the app), let it run, and every address comes back tagged with its result. The addresses that are safe to send to are gathered into a clean list you can point a campaign straight at — no exporting and re-uploading a trimmed spreadsheet. That flow is covered step by step in how to apply a cleaned list to a campaign.

Checks run at a steady, deliberate pace rather than all at once. That's on purpose: hammering a receiving mail server produces worse answers, not faster ones.

What each result means

Every address you check comes back as exactly one of these four:

A longer walk-through of each result, with the reasons behind them, is in what your verification results mean.

Why a catch-all address can't be resolved — by anyone

Some companies configure their mail server to accept mail sent to any address at their domain, whether or not that specific mailbox exists. These are catch-all domains, and they are the single honest limit of email verification.

Here's why. Verification works by asking the receiving server whether it would accept mail for an address. On a catch-all domain the server says yes to everything — a real person, a retired employee, a typo, a made-up name. The answer carries no information about that particular mailbox. No verification tool, ours or anyone else's, can get around that, because the information simply isn't there to be had. Any service claiming certainty on a catch-all address is telling you something the receiving server never told it.

So the verifier does the honest thing: it detects catch-all domains and flags those addresses as Risky, rather than passing them off as confirmed. That's a setting on the receiving end, not a fault in your list, and many catch-all addresses are perfectly deliverable. Knowing which ones they are lets you decide deliberately — send to them gradually through a well-warmed mailbox, hold them back, or work your confirmed-valid contacts first.

Why verify before sending

Bounces damage domain reputation. When you send to addresses that don't exist, mailbox providers see a spike in bounces and start treating your domain as a low-quality sender — which pushes even your good mail toward spam. Verifying first breaks that cycle:

• Protect sender reputation. Removing invalid addresses before you send keeps your bounce rate low and your domain trusted.
• Keep bounce rates low. A cleaner list means more of your emails reach the inbox and fewer get filtered.
• Protect the work you put into warmup. Warmup builds your reputation up; a batch of bounces can tear it down. Verifying keeps the two working together.

One honest caveat: a check reflects the moment it runs. Mailboxes get closed and people leave companies, so even a freshly cleaned list bounces a little — that's normal, not a failure. Why a verified list can still bounce covers what to expect and when to re-check.

What it costs — three ways in

You do not need a subscription to use the email verifier.

1. One free check a day — free, no account

Anyone can check a single address once a day at no cost, with no account and no card. It's the same check and the same four results a paid check returns — just one address at a time. Full details in using the email verifier without a plan.

2. Verification credits — no subscription needed

When you have a list to clean, buy a one-time pack of credits. No plan, no recurring charge:

• Credits never expire. A pack stays on your account until you use it — no monthly reset, nothing lost if you don't finish it in one sitting.
• One credit per confirmed address. A credit is spent when an address comes back valid, invalid or risky. Unknown results cost nothing — we don't charge for an answer we couldn't reach.
• Credits clear a big list today. They're additive on top of any plan allowance rather than capped by it, and they aren't held to the plan's gentle daily pace.

The 360,000-credit pack at $237 works out to $0.66 per 1,000 — the sweet spot for most list cleanups. All packs are on the pricing page and inside the verifier itself.

3. Included with any plan

If you're already running cold email campaigns on WarmySender, the verifier comes with your plan at no extra charge, with a monthly allowance that resets each month:

The plan allowance is spread gently across the month rather than released all at once, which keeps results accurate. Credits sit alongside it and skip that pace, so the two work together: use the allowance for steady upkeep, buy credits when a big list needs clearing today. The mechanics are set out in the guide to email verification limits and credits.

How it fits — verify, warm up, send

Verification is worth the most when it's the first step of a deliverability-first workflow, and the whole workflow runs in one place:

1. Verify. Check your list so you keep only addresses that are safe to send to, and flag the risky ones.
2. Warm up. Keep email warmup running on your mailboxes so they build and hold a strong sender reputation.
3. Send. Launch your cold email campaign to a clean list from a warmed-up mailbox — the combination that lands in the inbox.

The same prospects can also be reached on LinkedIn, or in a multichannel sequence that mixes both, so a reply on either channel stops the follow-ups on the other. And your contacts can come straight from the built-in B2B lead database — build the list, verify it, warm up, send, without leaving the platform.

Frequently asked questions

How do I check if an email address is valid?

Run it through an email verifier. Paste the address into WarmySender's email verifier and it asks the receiving mail server whether that address can actually receive mail, then reports one of four results: valid (exists, safe to send), invalid (doesn't exist — remove it), risky (usually a catch-all domain, where no tool can confirm one specific mailbox), or unknown (no confident answer this time — free, and not a sign the address is bad). One free check a day is free with no account, and there's no reliable way to do this by eye: an address can look perfectly well-formed and still bounce.

Can I use the email verifier without a subscription?

Yes. One free check a day is free with no account and no card. To check a list, you can buy one-time verification credits from $79 for 100,000 — no plan and no recurring charge, and the credits never expire. A WarmySender plan also includes a monthly verifier allowance at no extra cost, but a plan is one way in, not the only one.

How many free checks do I get?

One free check every day, and it resets the next day. It's a single-address check, it needs no account and no card, and it returns exactly the same result a paid check returns. When you need to check more than that at once, one-time credits start at $79 for 100,000 and never expire.

Do verification credits expire?

No. One-time verification credits never expire — they stay on your account until you use them, with no monthly reset and nothing lost if you don't finish a pack in one sitting. One credit is spent per confirmed result (valid, invalid or risky), and unknown results don't cost a credit. Credits are additive on top of a plan's monthly allowance rather than capped by it, and they skip the plan's gentle daily pace, so a pack can clear a big list today.

What happens if you can't tell whether an address is valid?

You aren't charged. Some receiving mail servers won't give a definite answer — that comes back as unknown, and an unknown result never uses a credit and never counts against a plan allowance. It's not a sign the address is bad: it usually means the answer wasn't available at that moment. Most unknowns are safe to email with warmup running, and re-checking later often produces a firm answer.

What do valid, invalid, risky and unknown mean?

Every address you check comes back as exactly one of four results. Valid means the address exists and can receive mail — safe to send. Invalid means it doesn't exist or can't receive mail — remove it. Risky usually means a catch-all domain — the receiving mail server accepts every address, so this exact mailbox can't be confirmed one at a time; many are still deliverable, so send gradually with warmup on. Unknown means a confident answer couldn't be reached this time — it's free (it doesn't use a credit) and usually safe to email with warmup running, or re-check later.

What is a catch-all domain, and why can't it be verified?

A catch-all domain is a company whose mail server is set to accept mail sent to any address at that domain, whether or not the specific mailbox exists. Because the server accepts almost anything, its answer tells you nothing about one particular mailbox — so no verification tool can confirm an individual address on a catch-all domain, ours included. That's a limit of the information the receiving server gives out, not a shortcoming in your list, and many catch-all addresses are perfectly deliverable. The verifier flags them as Risky rather than guessing, so you can decide whether to send to them gradually through a well-warmed mailbox or hold them back.

Why verify before sending?

Sending to addresses that don't exist causes bounces, and bounces damage your domain's reputation with mailbox providers — which pushes even your good mail toward spam. Verifying first lets you remove invalid addresses before they ever cost you, keeping your bounce rate low, your reputation intact, and more of your emails in the inbox. A check reflects the moment it runs, so re-check lists that have been sitting for a while.

Can the verifier get me an address I don't have?

No — and it's worth being straight about it. The verifier checks addresses you already have; it never produces one you're missing. If a contact has no address, there are two real paths: import a list that already includes the addresses, or save contacts from the built-in B2B lead database, where searching is free and the address is revealed when you save the contact.

Can an AI agent verify emails via API?

Yes. WarmySender offers a public REST API and an MCP server, so an AI agent (such as Claude or ChatGPT) can verify email addresses for you and act on the results — the same verification you'd run in the app, driven by your assistant in plain language.

How does the verifier fit with warmup and campaigns?

It's the first step in a deliverability-first workflow: verify your list to keep only safe-to-send addresses, keep email warmup running so your mailboxes hold a strong reputation, then send your campaign from a warmed-up mailbox to a clean list. Your contacts can come straight from the built-in lead database, so the whole flow — build the list, verify, warm up, send — happens in one place.

Check an address now

Paste an address and get your answer — one free check a day, free, no account. When you're ready to clean a whole list, credits start at $79 for 100,000 and never expire.

• Using the email verifier without a plan — the free daily check and buying credits with no subscription
• What your verification results mean — a deeper look at valid, invalid, risky and unknown
• Email verification limits & credits — how the plan allowance and one-time credits work together
• Why a verified list can still bounce — what a point-in-time check can and can't promise
• B2B lead database — build a contact list, then check it before you send
• Pricing — plans and one-time verification-credit packs
• Support — ask us a question, with or without an account