Can I validate email addresses in a CSV without uploading it?+
Yes. This validator parses the CSV or one Excel sheet in the browser tab, checks every address in the chosen column against syntax and length rules, and builds clean and flagged lists locally. Nothing is sent to a server.
Does a valid result mean the email will be delivered?+
No. Syntax validation proves only that an address is well-formed. It cannot prove that the domain accepts mail, that the mailbox exists, or that the person agreed to receive email. Confirmation messages and bounce handling in your sending platform answer those questions.
Which syntax rule does the validator use?+
The default is the WHATWG HTML definition of a valid email address, the same rule browsers apply to an email input. An optional stricter baseline adds the RFC 5322 dot-atom rule that forbids leading, trailing, or consecutive dots in the local part.
How long can an email address be?+
RFC 5321 sets 64 octets for the local part and 255 octets for the domain, and limits a path to 256 octets including its angle brackets. A verified erratum to RFC 3696 explains that this leaves 254 octets for the address itself.
Does the validator check MX records or disposable domains?+
No. It performs no DNS, MX, SMTP, or disposable-domain lookup, so it never contacts a mail server or reveals your list to a third party.
Are uppercase and lowercase duplicates the same address?+
The domain is case-insensitive. RFC 5321 says the local part must be treated as case-sensitive, even though most mailbox providers ignore case. The validator blocks exact duplicates and flags case-only duplicates for review.