Free for cold emailers, agencies and newsletter owners
Clean your email list before it burns your domain
Bounces and spam traps get a sending domain blocked. Drop your list here: every address is checked for syntax, dead domains, domains that refuse mail, disposable providers, typos and duplicates. The addresses stay in your browser; only the domains are looked up in DNS.
Is your sending domain ready?
A clean list is half the job. The other half is SPF, DKIM and DMARC on the domain you send from.
What is checked
Syntax and duplicates
Practical address syntax, and duplicates including Gmail dots and +tags, which land in the same mailbox.
The domain accepts mail
Each unique domain is looked up in DNS: MX records, a null MX that refuses all mail (RFC 7505), the A-record fallback (RFC 5321) and domains that do not exist.
Disposable, typos, roles
Over 9,900 disposable domains (public CC0 list), typo fixes for popular providers (gmial.com → gmail.com), and role accounts such as info@ that complain more often.
What it does not check yet
Whether a specific mailbox exists. That needs a short SMTP conversation with the recipient’s server from a server with a good reputation, which is the next step of this tool. Leave your email and I will tell you when it is ready.
Your list stays with you
- The file is read in your browser. Addresses are never sent to the server; only the unique domains are, to look them up in DNS.
- Domain results are cached for a day so repeated checks are fast. A daily counter of checked domains per network (hashed IP) is kept for 3 days to enforce the free limit; nothing else is stored.
- Analytics records only counts (how many rows, how many removed), never addresses or domains.
Sending at volume and want it to land in the inbox?
List hygiene is one part. I build the rest: sending domains and DNS, warm-up, suppression lists, bounce and complaint handling, and the integrations between your CRM and the sending tool. I built and ran a mail product that sent millions of messages.
Email infrastructure: price and start date → More about email work
Questions
Is it really free?
Yes, up to 50,000 addresses per check and 20,000 unique domains a day. It is how I show what I build.
Why not check every mailbox now?
Mailbox checks need an SMTP conversation on port 25 from a server with a clean reputation, which cloud platforms block by default. It is coming as the next step; the checks here already catch dead domains, typos and disposable providers, which cause most hard bounces.
What should I do with "risky" addresses?
Role accounts and free mailboxes are valid but complain more on cold email. Send to them carefully, in smaller batches, or leave them out of cold campaigns.
Is my list uploaded anywhere?
No. Open the browser network tab while it runs: only lists of domains are sent.
Who built it?
Przemysław Zalewski, an independent engineer. Check your sending domain with the free SPF, DKIM and DMARC checker.
