Email Address Validator
Enter one email address per line to validate them in bulk.
Enter email addresses above to validate them
Why validate email addresses before using them?
Invalid email addresses in a database cause bounce rates to climb, damage your sender reputation, and waste money on transactional email credits. Whether you are cleaning a legacy list, validating form submissions, or checking a CSV export before an import, catching bad addresses at the format level is the fastest and cheapest first step.
AlteredIdea's email validator applies the same structural rules that mail servers use before even attempting delivery: it checks local-part length, character legality, the presence of a domain, and a minimum TLD. That catches typos like missing @ symbols, double dots, and domains without a TLD: the most common classes of bad data in real-world lists.
How to validate: step by step
- 1Paste your email addresses
Type or paste one email address per line into the input textarea. You can paste a raw list from a spreadsheet, CRM export, or text file. - 2Results appear instantly
As you type or paste, every line is validated in real time. No submit button needed. - 3Review pass/fail badges
Each email gets a green 'Valid' or red 'Invalid' badge. Invalid entries show the exact reason: such as 'Missing @ symbol' or 'Domain has no TLD'. - 4Copy the valid list
Use the 'Copy valid' button in the summary bar to copy only the passing email addresses to your clipboard in one click. - 5Discard or fix the invalid ones
Use the 'Copy invalid' button to get only the failing addresses so you can correct them or remove them from your list.
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Frequently Asked Questions
- What validation rules does this tool apply?
- The validator checks that the address contains exactly one @ symbol, that the local part (before @) is no longer than 64 characters, that the full address is no longer than 254 characters, that the domain contains at least one dot, and that the overall format matches the RFC 5321 pattern for allowed characters.
- Does it verify that the email address actually exists?
- No. This is a format and syntax validator only. Checking whether a mailbox actually exists requires an SMTP handshake or an email deliverability API: those involve sending network requests, which this tool intentionally does not do.
- What is the maximum number of emails I can validate at once?
- There is no enforced limit. The validator processes every non-empty line you provide. For typical use cases: hundreds or low thousands of addresses: validation is instantaneous in any modern browser.
- Are subdomains and long TLDs supported?
- Yes. Addresses like [email protected] or [email protected] are accepted as valid, provided the rest of the format is correct.
- Why is an address like user@localhost marked as invalid?
- This validator requires the domain part to contain at least one dot and a TLD of two or more characters. Bare hostnames without a dot (like 'localhost') are not considered valid under the rules applied here.
- Does the tool handle plus addressing (e.g. [email protected])?
- Yes. The plus sign is a legal character in the local part under RFC 5321, so addresses using plus addressing for filtering: such as [email protected]: are marked as valid.
- Is my data sent to a server?
- No. All validation runs in JavaScript directly in your browser. Your email list never leaves your device.
- Why does a disposable or temporary email address pass validation?
- This tool validates syntax and format only, not reputation or disposability. Whether an address belongs to a disposable email provider is outside the scope of structural validation.
- Can I use this to clean a mailing list?
- Yes: paste your entire list, then use the 'Copy valid' button to extract only the syntactically correct addresses in one click. Keep in mind that passing format validation does not guarantee deliverability.
- What characters are allowed before the @ sign?
- The local part may contain letters (a-z, A-Z), digits (0-9), and special characters including . ! # $ % & ' * + / = ? ^ _ ` { | } ~ and -. Spaces and most other punctuation are not allowed.
AlteredIdea vs alternatives
vs regex testing manually: Instant validation with clear pass/fail feedback and explanation of why something is invalid.
vs library functions: No coding needed. Paste and validate instantly.
vs paid tools: Completely free, no account, unlimited checks.