What Is a Valid Email Address? Format, Examples, and Checks

A valid email address has a syntactically acceptable local part before the @ symbol and a valid domain after it. But valid format is not the same as a confirmed usable mailbox. An address can look correct and still point to a domain or mailbox that does not receive mail.

Valid Email Address Format

The basic structure is:

local-part@domain

For example:

• michael@example.com
• sarah.jones@company.co.uk
• first-last@subdomain.example.com
• user+filter@gmail.com
• contact_team@startup.io

The Local Part

The local part appears before the @ symbol. SMTP standards allow a maximum local-part length of 64 octets. In ordinary addresses it can contain letters, digits, and a range of permitted special characters. Period placement and quoting rules are more nuanced than many website regex patterns assume, which is why overly strict form validation can reject legitimate addresses.

The Domain

The domain appears after the @ symbol and identifies the mail domain. A syntactically valid domain still needs usable DNS and mail configuration before the address can receive normal email.

Examples of Invalid or Suspicious Formats

• user name@example.com - unquoted space in the local part.
• user@.com - invalid domain structure.
• user@ - missing domain.
• @example.com - missing local part.
• userexample.com - missing @ separator.

Some edge cases that look unusual can still be technically legal under email standards, so production forms should avoid simplistic regex rules that reject more than necessary.

Valid Format vs. Deliverable Mailbox

Syntax tells you only whether the address is shaped correctly. A fuller verification workflow can also evaluate the domain, MX configuration, mail-server responses, and risk signals.

For a single address, use the Free Email Checker. For the underlying process, see how email validation works.

Special Characters in Email Addresses

Many special characters are allowed in the local part under email standards, but support varies across applications and signup forms. Plus addressing such as name+tag@example.com is common and should not automatically be treated as invalid.

Internationalized addresses can also introduce non-ASCII characters under modern email standards. See international email verification for that edge case.

Email Address Length

RFC 5321 defines a maximum local-part length of 64 octets and a maximum domain length of 255 octets. The SMTP path limit is 256 octets including its delimiters, which is why a practical maximum mailbox string is commonly treated as 254 octets.

Common Mistakes in Signup Forms

• Overly strict regex. A form can reject legitimate plus addressing, long TLDs, or international formats.
• Checking syntax only. A correctly shaped address can still point to an unusable mailbox.
• Blocking role addresses as “invalid.” An address such as support@company.com can be technically valid even if your marketing policy treats it differently.
• Assuming disposable means invalid. A temporary mailbox can be technically deliverable while still being risky for your use case.
• Confusing a full inbox with an invalid address. Mailbox state and deliverability can change without making the syntax invalid.

How to Check an Email Address

One address

Use a single-address checker when you want to inspect one email quickly.

A file or database

Use bulk email verification when checking a CSV or TXT list.

A signup form or application

Use the Email Verification API when verification needs to happen inside a form, CRM, or automated workflow.

Frequently Asked Questions

Does a valid-looking address always receive email?

No. Correct syntax does not prove the domain or mailbox can receive mail.

Can an email address contain a plus sign?

Yes. Plus addressing is widely used and should not be rejected just because the local part contains +.

Are role addresses invalid?

No. Addresses such as info@, support@, or sales@ can be technically valid. Whether you want them in a marketing campaign is a policy decision, not a syntax decision.

Can I check one address for free?

Yes. Proofy's Free Email Checker is designed for single-address verification.

Bottom Line

A valid email address starts with correct syntax, but usability requires more than format. Keep syntax rules practical, avoid over-restrictive form validation, and use verification when you need evidence about the domain, mail infrastructure, or mailbox.