What is an email validator?
An email validator checks whether an email address could receive mail before you send anything to it. It tests the address in layers: is it written correctly, is the domain a real one, and has that domain published mail servers. Each layer catches a different kind of bad address, from a mistyped gmial.com to a company domain that expired years ago.
What the validator checks
- Format: one @, a name of up to 64 allowed characters, and a real-looking domain.
anna..b@x.comoranna@xfail. - Typos: slips such as
gmial.comorhotmail.coare caught with a suggested fix. - Domain: the domain must exist in DNS.
- Mail servers: the domain needs MX records; a “null MX” says it never takes mail.
- Throwaway and role addresses are flagged so you can decide whether to accept them.
What the results mean
| Result | When you see it | What to do |
|---|---|---|
| Valid | Correct format, the domain exists and it has mail servers | Safe to use |
| Risky | A throwaway inbox service, or a domain with a website but no MX record | Accept with care, or ask for another address |
| Invalid | Bad format, a known typo, a domain that does not exist, no mail servers or a null MX | Ask the person to check and retype it |
A role address such as support@ is flagged but not marked risky: it is a working inbox, just usually a shared one.
Valid and invalid email address examples
Every verdict in this table comes from the same format check the tool runs:
| Address | Format | Why |
|---|---|---|
| anna.smith@example.com | Valid | Ordinary address |
| anna+news@example.com | Valid | Plus addressing, used to sort or filter mail |
| o'brien@example.com | Valid | Apostrophes and many other symbols are allowed |
| anna..smith@example.com | Invalid | Two dots in a row |
| .anna@example.com | Invalid | Starts with a dot |
| anna smith@example.com | Invalid | Contains a space |
| anna@example | Invalid | No top-level domain such as .com |
| anna@-example.com | Invalid | Domain starts with a hyphen |
| anna@@example.com | Invalid | Two @ signs |
| aaaaaaaaaaaa…aa@example.com | Invalid | Name part is 65 characters, over the 64 limit |
The rules come from RFC 5321 and RFC 5322. The standards also allow rare forms such as quoted names with spaces ("anna smith"@example.com), but almost no real mailbox uses them and many websites reject them, so the tool treats them as invalid.
Typos the validator catches
A misspelled domain is the most common reason a real person’s address bounces. These are the slips the tool recognizes, each with its suggested fix:
| Typed | Suggested fix |
|---|---|
| gmial.com | gmail.com |
| gmai.com | gmail.com |
| gamil.com | gmail.com |
| gmail.co | gmail.com |
| gmail.con | gmail.com |
| gnail.com | gmail.com |
| hotmial.com | hotmail.com |
| hotmal.com | hotmail.com |
| hotmail.co | hotmail.com |
| yahooo.com | yahoo.com |
| yaho.com | yahoo.com |
| yahoo.co | yahoo.com |
| outlok.com | outlook.com |
| outloo.com | outlook.com |
| iclod.com | icloud.com |
| icloud.co | icloud.com |
Why no tool can prove a mailbox exists
Some services claim to confirm that a mailbox is real by connecting to the mail server and asking whether it would accept a message, then hanging up before sending. That check is unreliable. Many domains are “catch-all” and say yes to every name; large providers often accept first and bounce later; some servers delay unknown senders on purpose; and repeated probing looks like a spammer harvesting addresses, which can get the checking server’s IP blacklisted. This tool stops at what public DNS can prove. The only certain test is a message the person has to act on.
How to validate email addresses in a sign-up form
- Check the format as the person types, with a clear message instead of a silent rejection.
- Suggest a fix for typos such as
gmial.com, but let the person keep what they typed: some unusual domains are real. - Look up the domain’s MX records on your server before saving the address.
- Send a confirmation link and only add the address to your list once it is clicked (double opt-in). This proves the inbox exists and that its owner wants your mail.
- Remove addresses that hard-bounce straight away, so they do not drag down your sender reputation.
When to validate addresses
Checking addresses before you save them keeps a mailing list clean: bounces from invalid addresses hurt your sender reputation, and enough of them can get your mail sent to spam. The most common real-world problem is a simple typo in the domain, which this check catches.
To see which provider handles a domain’s email, use the MX lookup; to check your own domain is set up to send, the DMARC checker.