Email Validator (syntax + common typo detection)

What this validator does (and what it can't)

Email syntax validation checks whether 'name@domain.tld' follows the structural rules in RFC 5322. We use a pragmatic regex that catches almost all real-world typos while staying flexible enough for legitimate addresses with plus tags, dots, and unusual TLDs.

What this can NOT do: confirm the address actually receives mail. That requires sending a real email or doing an SMTP check, both of which require server-side code and risk false positives (catch-all domains, greylisting). Syntax validation catches typos cheaply; deliverability checks need a different approach.

Common typo detection

We watch for typos in the major free email providers — 'gmial.com' instead of 'gmail.com', 'yaho.com' instead of 'yahoo.com', etc. About 95% of email signup typos are domain typos in these few providers. Catching them client-side saves you a bounced welcome email and an uncomfortable 'please check your address' follow-up.

If you're building a signup form, run this same logic before submitting. Show a 'Did you mean…?' suggestion and let the user accept or override. Mature signup flows do this routinely; it noticeably improves email deliverability.

Local part rules

Plus tag ('user+filter@gmail.com'): widely supported by major providers. Use to create unique addresses for different sign-ups while keeping a single inbox.

Dots ('user.name@gmail.com'): treated as the same address by Gmail (dots are ignored), but other providers may treat them as different addresses. Don't rely on dot-equivalence outside Gmail.

Length: RFC 5321 limits local part to 64 chars and the full address to 254 chars. We warn when these are exceeded — most servers reject longer addresses.

Case sensitivity: per RFC, local part is case-sensitive but most providers treat it as case-insensitive. Domain is always case-insensitive.