EN

Validate Email Address Syntax

Paste one or more email addresses – one per line. For every line the tool shows whether the spelling follows the internet standards and gives the reason if it does not. It checks syntax only, not whether the mailbox exists.

“Name <address@example.com>” works too. Empty lines are skipped.

Your text stays in your browser – it is not sent, not stored and not added to the address bar.

Result

Result
1 valid, 4 with a note, 2 invalid (of 7)
Result per line
InputResultReason / note
jane.doe@example.com✓ valid syntax
Jane Doe <jane@example.org>⚠ allowed, but unusualdisplay name removed, only the address in < > was checked
info@müller.example⚠ allowed, but unusualdomain with accented letters – technically xn--mller-kva.example
"john doe"@example.com⚠ allowed, but unusualpart before the @ in quotation marks – allowed, but rejected by many services
wrong@@example.com✗ invalidcharacter not allowed before the @ (e.g. a second @, brackets, comma, quotation mark)
name@example..com✗ invalidempty domain label (two dots in a row or a dot at the start/end)
admin@localhost⚠ allowed, but unusualdomain without a dot – only reachable on a local network
Syntax only – the tool does not check whether the mailbox exists or the domain accepts email. Nothing is sent.

How it is calculated

The tool checks spelling only. Whether the mailbox exists, whether the domain accepts email or whether an address is disposable can only be found out by contacting the mail server – which this tool deliberately does not do. Your addresses stay in your browser; nothing is sent and nothing is stored.

What makes an email address valid

An address consists of a local part, an @ and a domain. The check follows the mailbox syntax of RFC 5321 – the way a mail server accepts a recipient address:

Accented letters in email addresses

Domains with accented letters (müller.de) are allowed: technically they are rewritten in Punycode (xn--mller-kva.de), and the tool shows that form. Non-ASCII letters before the @ can only be delivered with the SMTPUTF8 extension (RFC 6531), which by no means every server supports.

What is deliberately not accepted

Comments in parentheses and obsolete forms that RFC 5322 only keeps for reading old messages do not belong in recipient addresses and count as invalid here. Addresses without a dot in the domain (admin@localhost) and IP addresses in square brackets are formally correct, but not deliverable on the internet or unusual.

Frequently asked questions

Does the tool check whether an email address exists?

No. It checks syntax only. The only reliable proof that a mailbox exists is a delivered message – for example a confirmation link (double opt-in).

Are capital letters allowed in email addresses?

Yes. The domain is not case-sensitive. The part before the @ could be according to RFC 5321, but practically all providers treat upper and lower case the same.

Can an email address contain a plus sign?

Yes, name+newsletter@example.com is valid. Many providers use the plus for sub-addresses. If a form rejects it, the form is at fault.

How long can an email address be?

At most 64 characters before the @, 63 per domain label and 254 for the whole address (RFC 5321, section 4.5.3.1).

Can I check a whole list?

Yes, up to 1,000 lines at once – one address per line. Duplicates are flagged.

Sources and legal basis

As of:

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