About the Email Validator
Each address is checked against the rules that mail servers actually enforce. From RFC 5321: at most 64 characters before the @, at most 254 in total, and a domain made of labels of up to 63 letters, digits or hyphens that do not start or end with a hyphen. From RFC 5322: the local part may use letters, digits and !#$%&'*+/=?^_`{|}~-, with dots allowed only between other characters — so anna..lee@ and .john@ are rejected. Quoted local parts, IP-address literals and non-ASCII addresses are technically valid but flagged for review, because many sign-up forms and servers refuse them.
Beyond syntax, the checker looks for mistakes that pass a regular expression but still bounce: misspelled popular domains (gmial.com, hotmial.com) and top-level domains (.con, .cmo), known disposable-mailbox services, and role accounts such as info@ or noreply@. For Gmail addresses it shows the canonical form, because Gmail ignores dots and everything after + — useful for spotting duplicate sign-ups.
Syntax checks run entirely in your browser. The optional Check MX records button sends only the unique domain names to Cloudflare's DNS-over-HTTPS resolver and reports whether each domain publishes MX records, falls back to an A record, declares a null MX, or does not exist. No tool can prove a mailbox exists without contacting the receiving server, which is why results are labelled “valid syntax”, not “deliverable”.
How to use it
- Paste addresses into the box — one per line, or separated by commas or semicolons.
- Review the summary counts and the notes for each address.
- Optionally click “Check MX records” to see whether each domain accepts mail.
- Copy the valid addresses, or download the full report as CSV.