International email checker: IDN, punycode and non-ASCII addresses
An international email checker handles addresses with accents or non-Latin letters. A domain such as münchen.de is sent as xn--mnchen-3ya.de (punycode). A non-ASCII name before the @ needs SMTPUTF8 on every server on the route. Paste a list to see each domain's ASCII form and which addresses mix alphabets, a common look-alike trick.
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
How do I convert an international email address to punycode?
- Paste the addresses, one per line.
- Press Check the addresses.
- Read the ASCII form of each domain, and which addresses have a non-ASCII name before the @.
- Download the CSV with the ASCII domain and address for your sending system.
- Then check which mailboxes exist. Sign in with Google for the free email checks.
What is an internationalised email address?
It is an address with characters outside plain ASCII, in the domain, the name before the @, or both. The domain part is handled by Internationalised Domain Names: the visible name is converted to an ASCII form starting with xn--, called punycode (RFC 3492), and DNS only ever sees that form. So info@münchen.de is delivered through info@xn--mnchen-3ya.de, and the same domain is meant.
The name before the @ is different. A non-ASCII name needs the SMTPUTF8 extension (RFC 6531) on each server along the route, and many systems still reject or mangle such addresses.
Why does this matter for a mailing list?
Many platforms and databases store only the ASCII form, or reject accented addresses as invalid. Converting the domain to punycode before import avoids that for the domain half. Addresses with a non-ASCII name are the ones to test with the platform first, or move to a plain-ASCII alias.
It also affects safety. Domains that mix scripts, for example a Latin word with a Cyrillic letter that looks identical, are a well-known look-alike technique. The tool flags these so you can check them, as with the lookalike domain checker.
Who uses this tool, and for what?
- Marketers
- Prepare a European or Asian list for an email platform that stores only ASCII domains.
- Developers
- Normalise addresses before saving them, and know which ones need SMTPUTF8.
- Security teams
- Spot sign-ups whose domain mixes alphabets.
What can’t this tool tell you?
- Conversion uses the browser's own IDNA handling; unusual characters may be rejected as invalid.
- Converting a domain does not show the mailbox exists.
- Whether a given provider accepts a non-ASCII name before the @ is not tested here.
- Mixed-alphabet detection is a warning, not proof of abuse; some real names mix scripts.
Common questions
- How do I convert an email domain to punycode?
- Paste the address above. The domain part is converted to its xn-- form with the browser's IDNA handling.
- Can you send email to an address with accents?
- To an accented domain, yes, through its punycode form. To an accented name before the @, only if every server on the route supports SMTPUTF8.
- What does xn-- mean in a domain?
- The domain label is internationalised and encoded in punycode. The part after xn-- encodes the non-ASCII characters.
- Is a mixed-alphabet domain dangerous?
- It can be a look-alike of a trusted brand, so check it. Some legitimate names mix scripts.
- Is my list uploaded?
- No. The conversion happens in your browser.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
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