001INPUT
Paste the address
Drop any email into the pill. Gmail, Outlook, custom domains, role aliases. Single address now, bulk CSV on signup.
Continuous Deliverability Watch
Email Deliverability Monitoring That Catches Decay Before It Bounces.
The mail monitor for email deliverability that re-runs MX, SMTP, mailbox, and SPF, DKIM, DMARC checks on every address. Same 9-point engine as our paid API, 99.99% accuracy. No signup, no card.
Trusted by 500,000+ leading GTM teams of all sizes
Baseline, sweep, repeat
How email deliverability monitoring works here
Baseline any address in two seconds with the nine-check engine, sweep the whole list by CSV or API, then repeat on your cadence. Anything that flips to undeliverable gets flagged before it can bounce.
002ENGINE
Run the 9-check engine
Nine checks fire in parallel. Syntax, DNS, SMTP, catch-all, disposable, role, age, auth, mailbox state. Verdict in about two seconds.
003VERDICT
Verdict in 2 seconds
Valid, invalid, or risky. Plus a confidence score, the per-check breakdown, and a recommended retry policy. Read on the page or via API.
The 9-point engine
Nine checks. One verdict.
The same nine-check engine our paid email verification API runs. Every email, every verification, every time.
- 01
Syntax
Every address runs a full RFC 5321 and RFC 5322 compliance pass before a single network call goes out. The engine catches what visual scanning misses, the double dot in
alice@verifox..ai, the trailing period, the IDN homograph that looks valid but resolves to a different domain.Bundled typo suggestions let your form offer “did you mean alice@gmail.com?” instead of rejecting silently.
- 02
Domain & MX
Once syntax passes, the engine resolves the domain. We confirm the DNS records exist, fetch the MX record priority list in order, and verify at least one mail-exchange server is actively accepting connections right now.
Misspelled domains like
gmial.com, expired domains, and parked-for-sale domains all fail this gate before the engine wastes a single SMTP roundtrip.
- 03
SMTP handshake
The engine opens a TCP connection on port 25, performs the EHLO handshake, then negotiates
MAIL FROMandRCPT TO. Every server response code (220, 250, 550, 552) is parsed deterministically against the IANA enhanced-status registry.This is the moment a mailbox proves it actually exists. No third-party guesses, no statistical heuristics, just the receiving server's own answer.
- 04
Catch-all detection
Some domains accept every email regardless of whether the mailbox exists, a setup known as a catch-all configuration. The engine sends a deterministic probe to a deliberately fake address (
zzz9k7q@domain.com); if the server returns the same 250 OK it returned for the real address, the domain is catch-all.The verdict isn't dropped, it's flagged RISKY so you know the deliverability signal is degraded.
- 05
Disposable
The engine maintains a curated registry of 10,247 disposable email providers, including Mailinator, Guerrilla Mail, 10MinuteMail, Tempmail, and the long tail of regional clones.
Any address matching the blocklist is flagged INVALID. Deliverability to a mailbox that exists for 10 minutes and is never checked is functionally zero, regardless of whether the SMTP handshake passes.
- 06
Role address
info@,support@,no-reply@,admin@,hello@,billing@,contact@. These are shared inboxes, not individuals.The engine extracts the local-part of every address, matches it against the known role-prefix registry, and tags the result with a reduced engagement score.
You don't drop them automatically. The verdict tells you they're roles so you can decide whether they belong in your outbound.
- 07
Domain age
Fresh-spam domains registered hours ago are the single biggest source of inbound abuse. The engine queries WHOIS and RDAP for every unique domain, extracts the registration date, and flags anything under 30 days old with a “fresh” warning.
Domains aged 5+ years pick up a corresponding trust signal. The same heuristic spam filters have been using since the early 2000s, ported into the verdict.
- 08
Email authentication
SPF, DKIM, and DMARC together prove the sender is authorised to send from that domain.
The engine reads each policy via DNS, validates SPF includes recursively, scans six common DKIM selectors for a published key, and confirms DMARC alignment with the
From:header.A failing DMARC policy means the sender can be spoofed, so the verdict warns you before you reply.
- 09
Mailbox state
Beyond “exists vs doesn't exist”, the engine extracts the precise mailbox state from the SMTP server's response. Full inbox (552 / 522 quota), disabled mailbox (550 5.1.1), out-of-office autoresponder, frozen account.
Each state maps to a specific retry policy. Full inbox retries in 6 hours. Disabled drops permanently. The verdict tells you which bucket the bounce belongs in so your retry logic doesn't waste cycles.
The failure catalogue
What breaks between one-off checks
Deliverability rarely fails loudly. It erodes in five quiet ways, and each one maps to a specific check in the monitoring sweep.
Dead mailboxes piling up
Contacts change jobs and their inboxes get retired, but your CRM keeps mailing them. The first symptom is a hard-bounce spike on a campaign you cannot take back.
The check that catches it
The SMTP handshake and mailbox ping confirm each inbox still answers. Sweeping a list ahead of the send is exactly what the email bounce checker framing of this engine exists for.
Catch-all domains hiding the bodies
A catch-all server accepts every probe a basic verifier sends, so the address looks fine right up until the message dies inside the company's mail system. 20 to 40% of B2B lists fail here.
The check that catches it
Catch-all detection plus an AI-confidence pass on each catch-all address. The catch-all email checker runs this resolution standalone.
SPF SoftFail after a DNS edit
Someone adds a new SaaS sender, rewrites the SPF TXT record, and quietly breaks it. Mail that authenticated on Monday lands in quarantine on Tuesday.
The check that catches it
The authentication check validates SPF on every pass. Confirm a fix in isolation with the DMARC, DKIM and SPF check.
DKIM selector and DMARC alignment drift
A rotated key or a third-party sender signing with the wrong domain breaks alignment. DMARC starts failing while every dashboard you watch stays green.
The check that catches it
DKIM and DMARC validation in the same authentication leg. The DKIM tester isolates the selector when you need to debug one signature.
MX records orphaned by a migration
A domain migration or provider switch drops an MX record, and replies to a whole segment start vanishing. Nobody notices until a prospect calls to ask why you went silent.
How we stack up
Verifox vs the alternatives
Same nine-check pipeline, the highest published accuracy, credits that never expire, and an MCP server no competitor offers. Head-to-head with the two providers our buyers shortlist.
| Feature | Verifox | NeverBounce | ZeroBounce |
|---|---|---|---|
| Published accuracy claim | 99.99% | 99.0% | 99.6% |
| Credits expire | Never | Yes | Never |
| Free credits on signup | 1,000–2,500 / one-time | 1,000 / monthly | 100 / monthly |
| Verify without signup | |||
| Catch-all resolution | AI confidence | Flagged only | AI scoring |
| Real-time API | |||
| Bulk CSV upload | |||
| MCP server for AI agents | |||
| SOC 2 + GDPR + CCPA |
What teams are saying
Built for the teams that ship outbound
Growth leads, marketers, and engineers running real campaigns on real lists. Specific numbers, specific tools they switched from, and a verified email address on every byline.
90% lower bill, 0.4% bounces
We were paying ZeroBounce a four-figure monthly bill and still landing 3% bounces on cold campaigns. Switched the pipeline to Verifox, dropped to 0.4% bounces, and cut the bill by more than 90%.
Thomas G.GTM Lead, Stripe
Catch-all finally has a verdict
Other tools flag 30% of our B2B list as 'risky catch-all' and leave the call to us. Verifox returns a real verdict on those addresses, with a confidence score. We send more, we send safer.
Brittany K.GTM Lead, HubSpot
Reputation rebuilt in 6 weeks
We had a Gmail spam-folder problem after a bad list import. Verifox cleaned the list and the warmup ran on the same engine. Back in primary inbox in six weeks. One vendor, half the cost.
Dale M.GTM Lead, Slack
0.7% bounce on 50k
Ran a 50,000-address outbound list through Verifox before our quarterly campaign. Bounces landed at 0.7%, sender reputation didn't move, replies were up 22% over last quarter.
Erica K.GTM Lead, Discord
MCP in 10 minutes
Their MCP server let me wire email verification directly into our internal Claude agent in about ten minutes. Zero glue code. No other vendor in this space has thought about that workflow.
Greg L.GTM Lead, OpenAI
10k/min held under 400ms
Tested Verifox at 10,000 verifications per minute on a Tuesday morning. Latency held under 400ms median, no soft failures, no rate-limit walls. The vendor we benched throttled at 2,000/min.
Rini V.Product Manager, Vercel
Hygiene that doesn't break pipeline
Our SDRs were enriching from three tools and 14% of the emails were invalid before they hit the sequencer. Verifox sits in the pipeline now and the team stopped seeing 'undeliverable' replies the next week.
Jonathan A.GTM Lead, MongoDB
Bulk that actually ships
Bulk upload, sorted CSV back in twenty minutes, plug into our growth stack. The half-day list-hygiene project per cohort turned into something the marketing intern runs on autopilot.
Emma F.GTM Lead, Linear
Scores you can act on
Verifox returns a 0-100 confidence score per address, not just a label. We thresholded at 75 for the cold sequencer, 60 for nurture, and our deliverability team finally has a knob they can tune.
David H.GTM Lead, Snowflake
90% lower bill, 0.4% bounces
We were paying ZeroBounce a four-figure monthly bill and still landing 3% bounces on cold campaigns. Switched the pipeline to Verifox, dropped to 0.4% bounces, and cut the bill by more than 90%.
Thomas G.GTM Lead, Stripe
Reputation rebuilt in 6 weeks
We had a Gmail spam-folder problem after a bad list import. Verifox cleaned the list and the warmup ran on the same engine. Back in primary inbox in six weeks. One vendor, half the cost.
Dale M.GTM Lead, Slack
MCP in 10 minutes
Their MCP server let me wire email verification directly into our internal Claude agent in about ten minutes. Zero glue code. No other vendor in this space has thought about that workflow.
Greg L.GTM Lead, OpenAI
Hygiene that doesn't break pipeline
Our SDRs were enriching from three tools and 14% of the emails were invalid before they hit the sequencer. Verifox sits in the pipeline now and the team stopped seeing 'undeliverable' replies the next week.
Jonathan A.GTM Lead, MongoDB
Scores you can act on
Verifox returns a 0-100 confidence score per address, not just a label. We thresholded at 75 for the cold sequencer, 60 for nurture, and our deliverability team finally has a knob they can tune.
David H.GTM Lead, Snowflake
Catch-all finally has a verdict
Other tools flag 30% of our B2B list as 'risky catch-all' and leave the call to us. Verifox returns a real verdict on those addresses, with a confidence score. We send more, we send safer.
Brittany K.GTM Lead, HubSpot
0.7% bounce on 50k
Ran a 50,000-address outbound list through Verifox before our quarterly campaign. Bounces landed at 0.7%, sender reputation didn't move, replies were up 22% over last quarter.
Erica K.GTM Lead, Discord
10k/min held under 400ms
Tested Verifox at 10,000 verifications per minute on a Tuesday morning. Latency held under 400ms median, no soft failures, no rate-limit walls. The vendor we benched throttled at 2,000/min.
Rini V.Product Manager, Vercel
Bulk that actually ships
Bulk upload, sorted CSV back in twenty minutes, plug into our growth stack. The half-day list-hygiene project per cohort turned into something the marketing intern runs on autopilot.
Emma F.GTM Lead, Linear
90% lower bill, 0.4% bounces
We were paying ZeroBounce a four-figure monthly bill and still landing 3% bounces on cold campaigns. Switched the pipeline to Verifox, dropped to 0.4% bounces, and cut the bill by more than 90%.
Thomas G.GTM Lead, Stripe
0.7% bounce on 50k
Ran a 50,000-address outbound list through Verifox before our quarterly campaign. Bounces landed at 0.7%, sender reputation didn't move, replies were up 22% over last quarter.
Erica K.GTM Lead, Discord
Hygiene that doesn't break pipeline
Our SDRs were enriching from three tools and 14% of the emails were invalid before they hit the sequencer. Verifox sits in the pipeline now and the team stopped seeing 'undeliverable' replies the next week.
Jonathan A.GTM Lead, MongoDB
Catch-all finally has a verdict
Other tools flag 30% of our B2B list as 'risky catch-all' and leave the call to us. Verifox returns a real verdict on those addresses, with a confidence score. We send more, we send safer.
Brittany K.GTM Lead, HubSpot
MCP in 10 minutes
Their MCP server let me wire email verification directly into our internal Claude agent in about ten minutes. Zero glue code. No other vendor in this space has thought about that workflow.
Greg L.GTM Lead, OpenAI
Bulk that actually ships
Bulk upload, sorted CSV back in twenty minutes, plug into our growth stack. The half-day list-hygiene project per cohort turned into something the marketing intern runs on autopilot.
Emma F.GTM Lead, Linear
Reputation rebuilt in 6 weeks
We had a Gmail spam-folder problem after a bad list import. Verifox cleaned the list and the warmup ran on the same engine. Back in primary inbox in six weeks. One vendor, half the cost.
Dale M.GTM Lead, Slack
10k/min held under 400ms
Tested Verifox at 10,000 verifications per minute on a Tuesday morning. Latency held under 400ms median, no soft failures, no rate-limit walls. The vendor we benched throttled at 2,000/min.
Rini V.Product Manager, Vercel
Scores you can act on
Verifox returns a 0-100 confidence score per address, not just a label. We thresholded at 75 for the cold sequencer, 60 for nurture, and our deliverability team finally has a knob they can tune.
David H.GTM Lead, Snowflake
Why monitor here
A mail monitor without the retainer
Deliverability monitoring services usually mean a monthly retainer and a PDF. Here the full nine-check engine the paid plans use runs on demand, capped only on volume, and your credits never expire between sweeps.
Accuracy
99.99%accuracy
The same nine-check engine
The free tier runs the full nine-check pipeline from our email verification API, capped on volume and never on accuracy.
Friction
0signups to begin
No signup to start
Verify your first emails right here with no signup at all. Create a free account when you go past four checks a day.
Coverage
10kemails / minute
API and bulk, included
Your free plan unlocks the very same REST API, CSV upload, and bulk parallel processing that the paid plans run on.
Privacy
SOC 2GDPR · CCPA
Emails are never stored
Addresses are processed in memory and dropped on response, nothing stored and nothing sold. Read the privacy policy.
Monitoring, explained
What email deliverability monitoring services actually watch
When senders go looking for mail monitor email deliverability services, the problem behind the search is almost always the same: a list or a domain that was healthy once, with nobody watching it since. Deliverability has two halves. The domain side covers blacklist listings and the reputation mailbox providers attach to your sending infrastructure. The address side covers whether the mailboxes you mail still exist and whether your authentication records still pass. Most monitoring retainers obsess over the first half and assume the second is fine. It usually is not: 20 to 40% of B2B email lists fail at catch-all domains, the one place a casual check cannot see.
This page is the address side, automated. Every sweep runs the same 9-point engine behind our email verification service: syntax, domain and MX records, a live SMTP handshake with a mailbox ping, catch-all detection with an AI-confidence score, disposable and role filters, domain age, and SPF, DKIM, and DMARC authentication. Verdicts measure 99.99% accurate on a 1,000-address benchmark. To improve email deliverability with a mail monitor workflow rather than a one-off scrub, schedule the sweep through the REST API; bulk passes run at roughly 10,000 emails a minute, and a single recheck returns in about 380 ms.
Cadence is what makes monitoring work. Re-verify before every meaningful send, monthly for lists you mail often, and pair the address sweep with the email blacklist check and domain reputation checker so the domain half is covered too. Credits are pay-as-you-go and never expire, with volume pricing localized to your region, so a disciplined monthly rhythm costs exactly what it uses and nothing more.
Trust & compliance
Enterprise-grade security and scale
Every layer of the stack carries a third-party attestation, so you can ship into regulated industries without rebuilding your compliance posture.
SOC 2 Type II
Independently audited to the SOC 2 Type II standard.
GDPR
Built for the EU with full GDPR data-subject rights.
CCPA
California opt-out, do-not-sell, plus DSAR handling.
ISO 27001
Information security held to the ISO 27001 standard.
ISO 42001
AI governance aligned to the new ISO 42001 standard.
Common questions
Deliverability monitoring, answered
What senders ask before they put a list under monitoring, answered with the actual numbers, the actual limits, and an honest line on what this service does and does not watch.
What is email deliverability monitoring?
Email deliverability monitoring means re-checking, on a schedule, the signals that decide whether your mail gets accepted: live mailboxes, valid MX records, a passing SMTP handshake, and SPF, DKIM, and DMARC authentication. A one-time list scrub answers those questions for a single day; monitoring keeps answering them as mailboxes die, DNS records change, and forms collect new junk.
Verifox runs nine checks per address on every pass, the same pipeline behind our email verification service, so a monitoring sweep is a full verification, not a cached lookup.
Is Verifox a mail monitor for email deliverability?
For the address and authentication side, yes. Classic mail monitor services watch your sending domain: blacklist listings and inbox placement panels. Verifox monitors what those services assume is already fine, whether the mailboxes on your list still exist and whether your SPF, DKIM, and DMARC records still pass.
The two halves complete each other. Run your sweeps here, then cover the domain-reputation side with the email blacklist check and the domain reputation checker.
Is the deliverability monitoring free to start?
Yes. The scanner on this page gives you 4 checks per day with no account and no card. That is enough to spot-check your own address and your highest-value contacts daily.
Sign up free and 1,000 credits land instantly, 2,500 if you register with a work address. From there credits are pay-as-you-go with volume pricing localized to your region.
Which deliverability signals does each monitoring pass cover?
Every address goes through nine checks in parallel:
- Syntax and format (RFC 5321 / 5322)
- Domain existence and MX records
- SMTP handshake and mailbox ping
- Disposable-domain match
- Role-address detection
- Catch-all detection, with AI-confidence scoring
- Domain age
- SPF, DKIM, and DMARC authentication
The authentication leg is the one most list tools skip entirely. If you only need that piece, the standalone DMARC, DKIM and SPF check runs it on its own.
How often should I monitor my list's deliverability?
Before every meaningful send, and at least monthly for any list you mail regularly. Addresses decay constantly: people change jobs, companies migrate domains, and inboxes get retired without notice. A list that verified clean a quarter ago is a different list today.
The expensive failure mode hides at catch-all domains, where 20 to 40% of B2B email lists actually fail. Those domains accept every probe a basic checker sends, so only the catch-all resolution with AI scoring catches the dead ones between sends.
Can I automate deliverability monitoring with the API or an AI agent?
Yes, that is how most teams run it. A scheduled job hits the REST API, sweeps the list at roughly 10,000 emails per minute on the standard tier, and routes anything that flips to undeliverable back into your CRM. Single checks return in about 380 ms, sub-50 ms when cached.
AI agents get the same engine with zero glue code through the native MCP server: point Claude, Cursor, or a custom agent at the MCP URL and the monitoring tools are wired.
Does monitoring cover my DNS and authentication records too?
Yes. The ninth check validates SPF, DKIM, and DMARC on the sending domain, and the MX leg confirms mail routing still resolves. DNS edits are the classic silent killer: one rewritten TXT record turns a passing SPF into a SoftFail, and nothing tells you until open rates sag.
For deeper single-purpose digging, the MX lookup, DKIM tester, and SMTP test each isolate one layer of the same stack.
What happens to the addresses I run through the monitor?
They are processed in memory and discarded the instant the verdict returns. Verifox never stores, logs, or sells the addresses you monitor, which matters when the list you are sweeping is your customer base.
The operation is SOC 2 Type II audited, and the privacy policy spells out exactly what is touched in transit. More than 2.1B emails have been verified under that model.
What does ongoing monitoring cost at volume?
One credit per address per pass, and credits never expire, so a monthly cadence wastes nothing if a sweep slips a few weeks. Volume rates step down as usage grows; exact numbers are shown for your region on the pricing page.
Uptime is backed by a 99.9% SLA on Starter and 99.99% on annual Volume contracts, with live status at status.verifox.ai.
How is monitoring different from a one-time deliverability test?
Same engine, different posture. A one-time deliverability test answers "is this address good right now?" Monitoring asks that question again next week, because the answer changes. The verdicts themselves are identical: deliverable, undeliverable, or risky, with a confidence score and a per-check breakdown.
If you want a single composite grade for an address instead of a recurring sweep, the email health checker frames the same nine checks as a one-shot report card.
Start monitoring
Put your list under watch before the next send
Sign up free and 1,000 credits land instantly, 2,500 with a work address. No card. One credit verifies one address, credits never expire, and your first full monitoring sweep takes minutes, not a sales call.