Email Domain Part Only Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching email domain part only, ported and verified for PHP. Identity and credential patterns need both correctness and safety, since they're frequent targets for adversarial input. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Email Domain Part Only
// ReDoS-safe | RegexVault — Identity & PII > Email Address

define('EMAIL_DOMAIN_PART_ONLY_PATTERN', '/^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\.[a-zA-Z]{2,}$/');

function validate_email_domain_part_only(string $input): bool {
    return (bool) preg_match(EMAIL_DOMAIN_PART_ONLY_PATTERN, $input);
}

// Example
var_dump(validate_email_domain_part_only("example.com")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Identity & PII > Email Address category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Domain labels are max 63 chars each. Total domain max is 253 chars. Underscores are not allowed in domain names (though common in hostnames). The TLD must be 2+ letters.