Email Syntax Validator
Validate email address syntax without contacting mail servers.
Overview
The email syntax validator checks whether an address is well-formed according to the actual mail standards — RFC 5321 envelope rules and RFC 5322 message-format rules — without contacting any mail server. It catches the obvious problems (missing @, illegal characters, overlong local parts) and the subtle ones (quoted strings, comments, internationalised domains).
Form designers tightening their sign-up flow, data engineers cleaning a CSV before import, and support teams sanity-checking a typo'd address all need email format checking without false positives. Long-tail keywords covered: validate email syntax without sending, check RFC 5322 email format, and email regex alternative.
How it works
A valid email address is a local part, an @, and a domain. The local part may be a dot-separated atom of allowed ASCII characters or a quoted string permitting almost anything. The domain may be a dotted DNS name or, less commonly, a literal IP address in brackets. RFC 6531 extends this with internationalised local and domain parts encoded in UTF-8.
Length matters: the local part caps at 64 octets, the domain at 255, and the whole address at 254 in practice. A correct validator uses a parser, not a single regex — the popular "RFC 5322 email regex" is hundreds of characters long and still incomplete. This tool walks the address character by character against the grammar.
Examples
alice@example.com→ valid, the canonical form."alice and bob"@example.com→ valid, quoted local part with a space inside.alice@[192.0.2.1]→ valid, IP address literal as the domain.alice..bob@example.com→ invalid, consecutive dots are not allowed in an unquoted local part.
FAQ
Does a passing check mean the mailbox exists?
No. Syntax validation is purely structural. The only way to confirm the address actually receives mail is to send to it (or use a third-party SMTP probe, which carries deliverability risks).
Should I reject addresses with + aliases?
No. alice+signup@example.com is perfectly valid and widely used. Many users rely on plus addressing to track which service leaked their email.
Are international domains supported?
Yes. The validator accepts both the Unicode form (alice@münchen.de) and the Punycode form (alice@xn--mnchen-3ya.de).
Why do some libraries reject alice@localhost?
Strict validators require at least one dot in the domain, treating bare hostnames as invalid for public email. RFC 5322 actually allows them, but they are useless for mail delivery across the internet.