Email Syntax Validator

What this tool does

Email Syntax Validator checks an email address’s structure against the practical syntax rules real mail servers enforce, local and domain part length limits, consecutive or leading/trailing dots, and a valid domain with a top-level domain, and lists any specific issues found.

An email address can look fine at a glance and still be structurally invalid, a stray double dot, a missing top-level domain, or a local part that’s simply too long for any real mail server to accept, none of which is obvious just by reading it.

This validator checks an address against the practical syntax rules real mail servers actually enforce, drawn from RFC 5321/5322, not the full, far more permissive grammar those RFCs technically allow, and lists the specific issue found when something is wrong, rather than just a pass/fail verdict.

How to use Email Syntax Validator

1. Enter the Email address you want to check.
2. Review the Syntax result and any Issues found.
3. Check the parsed Local part and Domain for a sanity check.
4. Fix any flagged issue and re-check until the syntax passes.

Tips for better results

• This checks structure only; it cannot and does not confirm the mailbox actually exists or can receive mail, that requires either an SMTP-level check or sending a real verification email.
• The 64-character local part and 255-character domain limits come directly from RFC 5321 and are enforced by essentially every real mail server, even though they’re rarely approached in everyday addresses.
• A missing dot in the domain (like name@localhost) is flagged, since a deliverable public email address always needs a top-level domain.
• Full RFC 5322 technically permits much stranger syntax (quoted local parts, embedded comments) than this checks for; this uses the practical subset that real-world providers like Gmail and Outlook actually accept.

Common use cases

• Validating an email field in a sign-up or contact form before accepting it.
• Debugging why a specific email address is being rejected by a form or system.
• Checking a list of addresses for obvious formatting errors before a bulk import.
• Understanding exactly which practical rule a malformed address violates.

Common mistakes to avoid

• Treating "valid syntax" as proof the address can receive mail; syntax validation and mailbox existence are two completely different checks, and only the second one actually confirms deliverability.
• Rejecting a technically valid but unusual address (like one with a plus-addressing tag, name+tag@example.com) due to an overly strict custom pattern; this validator accepts the common, real-world-valid characters mail providers support.
• Assuming every address without issues here is guaranteed deliverable long-term; even a syntactically perfect, currently-active mailbox can become invalid later.