Email Validator

How to use it

1. Paste addresses into the panel, one per line. A CSV column, a newsletter export or a hand-written list all work.
2. Leave Allow quoted local part on if your data contains addresses such as "first last"@example.com.
3. Turn on Allow domain literal when addresses like user@[192.0.2.10] should count as valid, which is rare in real mail lists.
4. Read the Results: every line starts with OK or FAIL, and every failure carries the specific reason.
5. Check the counter for totals, valid, failed, unique and duplicate entries, then Copy or Download the report.

Common use cases

• Cleaning a mailing list before an import - spot typos such as a missing @ or a truncated domain.
• Reviewing a signup form's validation - paste the addresses your form accepted and see which ones a stricter check rejects.
• Deduplicating an export - the unique and duplicate counts tell you how much of the list is repeated.
• Checking data from a spreadsheet - stray spaces, a trailing dot or a doubled @ show up with a reason.
• Teaching what an address may contain - each rule is reported separately, so the rules are visible in the output.

Why it stays private

Email lists are personal data, and a list of addresses is exactly what you should not paste into a random service. Every check runs with local string handling in the page, and no request is made while you validate.

FAQ

Q: Does this verify that the mailbox exists? A: No. That would require connecting to a mail server, which cannot be done from a browser page and would also be unreliable because most servers refuse such probes. This tool checks syntax only.

Q: Which rules are applied? A: One unquoted @ separator, a local part up to 64 characters with allowed atoms and no dot at the start, at the end or doubled in a row, a domain up to 255 characters with labels of 1 to 63 characters that do not start or end with a hyphen, and a final label of at least two letters.

Q: Why is an address with a long TLD rejected? A: The final label must be letters only. Anything else is a typo or a hostname that is not a registered top level domain, and both are worth reviewing before you mail them.

Q: Are uppercase addresses treated as duplicates? A: Yes. Duplicates are compared case-insensitively, which matches how the domain part is handled and catches the same address typed twice with different capitalization.