Valid characters in an email address (and the maximum length)
The email standards allow far more characters than most providers let you choose. Here are the official rules, what Gmail and Outlook.com actually allow, and the safe set to stick to.
The safe set is letters, numbers, dots, hyphens and underscores before the @. The standards also allow characters such as + ! # $ % & ' * / = ? ^ ` { | } ~. A dot cannot be first, last or doubled. The part before the @ can be up to 64 characters, and the whole address up to 254.
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The parts of an email address
name@example.com: the part before the @ is the local part (the mailbox name). The part after is the domain. Each has its own rules.
Characters allowed before the @
| Character | Allowed by the standard? | Notes |
|---|---|---|
| Letters a–z, A–Z | Yes | Most providers ignore capitals |
| Numbers 0–9 | Yes | |
| Dot . | Yes | Not first, not last, never two in a row |
| Hyphen - | Yes | Fine anywhere in the local part |
| Underscore _ | Yes | Gmail does not allow it in new usernames |
| Plus + | Yes | Often used for tags: [email protected] |
| ! # $ % & ' * / = ? ^ ` { | } ~ | Yes | Legal but rare; some websites wrongly reject them |
| Spaces, commas, ( ) < > [ ] : ; @ \ " | Only inside quotes | Quoted addresses are valid but almost never used. Avoid. |
Rules for the domain (after the @)
- Letters, numbers and hyphens, separated by dots: mail.example-shop.com.
- A hyphen cannot start or end a part of the domain: -example.com is invalid.
- Each part (label) can be up to 63 characters.
- Domains are not case-sensitive.
Maximum length
| Part | Maximum |
|---|---|
| Local part (before the @) | 64 characters |
| Each domain label | 63 characters |
| Whole address | 254 characters |
The standard's limit on the mail "path" is 256 characters including the angle brackets around the address, which leaves 254 for the address itself.
What Gmail and Outlook.com let you choose
| Provider | Allowed in a new username |
|---|---|
| Gmail | Letters, numbers and periods; 6–30 characters |
| Outlook.com | Letters, numbers, dot, underscore and hyphen |
Both will still receive mail from addresses that use other legal characters.
Can you have a hyphen or dash in an email address?
Yes. [email protected] is valid, and hyphens are common in company domains such as @smith-sons.com. Gmail is the main exception: you cannot pick a hyphen in a new Gmail username. When reading an address aloud, say "dash" or "hyphen" clearly, because it is easy to mishear.
Building a form? Validate gently
Strict format checks often reject real customers, especially those with + or ' in their address. A sensible check is: one @, something before it, a domain with a dot after it, and no spaces. Then confirm the address really works by sending a confirmation email. To test a list, use the free email checker.
Questions people ask
- Is an email address case-sensitive?
- The standard lets the part before the @ be case-sensitive, but in practice almost every provider, including Gmail and Outlook.com, treats capitals and small letters the same.
- Can an email address start with a number?
- Yes. Numbers are allowed anywhere in the local part, including the first character.
- Can an email address have two dots in a row?
- No, not without quotes. [email protected] is invalid.
- What is the shortest valid email address?
- In theory one character, an @, and a short domain, such as [email protected]. Many providers set their own minimum; Gmail requires 6 characters.
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