Format only
Email syntax checker
Check whether an email address is written correctly before you store it or send to it. This email format validator runs in your browser, explains every rule the address breaks and points out common domain typos like gmial.com.
The rules
What makes an email address valid in format
The format of an email address is defined by RFC 5321 and RFC 5322. These are the rules this email syntax validator applies, in the order it applies them.
| Rule | Passes | Fails |
|---|---|---|
| Exactly one @ separates the local part from the domain | Passes: [email protected] | Fails: ann.shop.com |
| No spaces anywhere in the address | Passes: [email protected] | Fails: ann [email protected] |
| Local part is 1 to 64 characters | Passes: [email protected] | Fails: @shop.com |
| Whole address is at most 254 characters | Passes: typical addresses | Fails: 255+ characters |
| A dot cannot start or end the local part, or appear twice in a row | Passes: [email protected] | Fails: [email protected] |
| Local part uses letters, digits and ! # $ % & ' * + / = ? ^ _ ` { | } ~ . - | Passes: [email protected] | Fails: ann,[email protected] |
| Domain has at least one dot and labels of 1 to 63 letters, digits or hyphens | Passes: [email protected] | Fails: ann@shop |
| A domain label cannot start or end with a hyphen | Passes: [email protected] | Fails: [email protected] |
| The top-level domain is letters only, at least two | Passes: [email protected] | Fails: [email protected] |
RFC 5322 also allows quoted local parts ("ann lee"@shop.com), comments and IP-address domains. They are legal on paper and rejected by almost every signup form and mail provider, so this checker flags them as Not Valid for practical use.
Format is step one
Email format validation vs email verification
Email format validation answers one question: is this string shaped like an email address? It is instant, free and catches typos, pasted junk and broken form input. It cannot tell you whether anyone reads the mailbox.
Email verification goes further. Mail7 looks up the domain's MX records, then holds a short SMTP conversation with the receiving server and asks about the one recipient, without sending a message. The answer is Valid, Not Valid or Unknown, and Unknown always comes with the reason the server would not say.
Use the syntax check in forms and spreadsheets as a first filter, and run a full email check before you send anything that matters. Developers can run both through the email validation API.
Questions
Email syntax checker FAQ
What is the correct format of an email address?
A local part, one @ sign and a domain: [email protected]. The local part is up to 64 characters of letters, digits, dots and a few symbols such as + and _. The domain is made of labels separated by dots and ends in a letters-only top-level domain.
Does a valid format mean the email address exists?
No. A format check only proves the address is written correctly. The domain may have no mail server and the mailbox may not exist. The free Mail7 email checker tests the MX records and the mailbox to answer that.
Is a plus sign allowed in an email address?
Yes. The + is a legal character, and Gmail, Outlook and many other providers use it for sub-addressing, so [email protected] delivers to [email protected]. Forms that reject the plus sign are wrong.
Can an email address contain uppercase letters?
Yes. The domain is case-insensitive, and in practice almost every provider treats the local part as case-insensitive too. Store addresses as entered and compare them in lowercase.
Are email addresses with non-English characters valid?
Internationalized addresses such as josé@exemple.fr are allowed by RFC 6531, but many mail servers still cannot deliver to them. This checker accepts them with a warning, and the full Mail7 check reports them as Unknown rather than guessing.
Is this email format checker free?
Yes, with no signup and no limit. It runs entirely in your browser, so the addresses you type are never sent to Mail7 or to any mail server.