What gets checked
| Syntax | One @, a non-empty part on each side, no spaces, no leading, trailing or doubled dots, and only the characters RFC 5322 allows before the @. The part before the @ may be at most 64 characters and the whole address at most 254 (RFC 5321). |
| Domain | At least one dot, labels of 1–63 letters, digits or hyphens that don't start or end with a hyphen, and a real-looking top-level domain. Reserved names such as example.com and .test are flagged because they can never receive mail. |
| Typos | Domains one or two keystrokes away from a big provider (gmial.com, hotmial.com, outlok.com, yahoo.con) get a "Did you mean" suggestion. |
| Disposable | The domain is compared with the same public list of about 10,000 temp mail domains that our disposable email checker uses. |
| MX (optional) | Whether the domain publishes mail servers, refuses mail outright (a "null MX") or doesn't exist. For the server names themselves, use the MX lookup. |
Valid, Check or Invalid
Valid means the address follows the rules and nothing looked off. Check means it's technically fine but probably not what the person meant, or it won't reach a real person for long: a typo suggestion, a temp mail domain, a role account, a plus address or a domain without MX records. Invalid means mail to it will bounce or be refused by most forms.
A "Valid" result is about the format and the domain. It doesn't prove the mailbox exists or that anyone reads it.
Common mistakes this catches
Most bad addresses in sign-up forms aren't fake. They're typed on a phone: a comma instead of a dot (jane@gmail,com), a space after autocomplete, a missing letter in the provider's name or .con instead of .com. If you run a newsletter or a shop, catching these at the form saves you a bounce and a lost customer. Showing a "Did you mean gmail.com?" hint fixes the typo without blocking anyone.
Lists copied from spreadsheets add their own problems: display names (Jane Doe <[email protected]>), mailto: prefixes and stray quotes. The validator strips the display name and the prefix and tells you it did.
Should you block disposable addresses?
Usually not outright. People use temp mail to protect themselves from spam, and many of them would sign up properly once they trust you. Our guide on how sites detect disposable email explains the trade-offs and the softer options, such as allowing the sign-up but asking for a long-term address before a free trial or payout.
Questions
Can this tell me if a mailbox really exists?
No, and no honest web tool can do that reliably. The only way is to connect to the receiving server and pretend to send mail (an SMTP 'ping'), which big providers like Gmail and Outlook deliberately answer with 'yes' for every address, and which gets the checking server blocklisted. The surest test is to send a confirmation email and see if someone clicks it.
Are the addresses I paste stored?
No. All the checks run in your browser. The disposable-domain list is a static file loaded from our site, and the optional MX lookup goes from your browser straight to Cloudflare's public DNS resolver, which only sees the domain name, never the full address.
Why is a valid-looking address marked 'Check'?
Because it's valid but something about it deserves a second look: a likely typo in the domain, a known temp mail domain, a role address like info@ that reaches a team rather than a person, or a domain with no mail servers.
Why do some sites reject my plus address when this tool says it's valid?
The + sign has been legal in addresses since the 1980s, but some sign-up forms use over-strict patterns. That's a bug in the form, not your address.