Standard Email Validation Regex (RFC 5322 Basic)

A comprehensive guide to the RFC 5322 basic email regex pattern ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ and how it works.

Pattern Breakdown

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

Components

Character Classes

• a-zA-Z - All uppercase and lowercase letters
• 0-9 - All digits
• . - Literal dot (in character class, doesn't need escaping)
• _ - Underscore
• % - Percent sign
• + - Plus sign
• - - Hyphen (must be at end or start of character class to avoid range interpretation)
• {2,} - Quantifier: two or more occurrences

Examples

Valid:

• user@example.com
• john.doe@company.org
• user+tag@domain.co.uk
• test_email@sub-domain.net
• user%name@example.info
• user_name@example-domain.com

Invalid:

• user@domain (missing TLD)
• @domain.com (missing local part)
• user@.com (missing domain)
• user name@domain.com (space not allowed)
• user@domain.c (TLD must be at least 2 characters)
• user@@domain.com (double @ symbol)

Implementation

JavaScript

const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
emailRegex.test('user@example.com'); // true
emailRegex.test('john.doe+tag@company.org'); // true

Python

import re
email_regex = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
bool(re.match(email_regex, 'user@example.com'))  # True
bool(re.match(email_regex, 'john.doe+tag@company.org'))  # True

Go

emailRegex := regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)
emailRegex.MatchString("user@example.com") // true
emailRegex.MatchString("john.doe+tag@company.org") // true

Limitations

1. Multi-part TLDs: Doesn't match .co.uk, .com.au (would need \.[a-zA-Z]{2,}(\.[a-zA-Z]{2,})?$)
2. No length validation: RFC 5322 limit is 320 characters total
3. No quoted strings: Doesn't support "user name"@example.com
4. No IP addresses: Doesn't allow user@[192.168.1.1]
5. No comments: Doesn't support user(comment)@example.com

When to Use

• Client-side form validation
• Basic format checking for most common email formats
• Quick validation before API calls
• When you need to support plus signs and percent signs in local part

For production, consider RFC 5322-compliant patterns or validation libraries, and always verify emails via confirmation messages.