5 Ways to Implement Email Validation in PHP

Validating email addresses in PHP is a fundamental step for maintaining data quality and ensuring reliable communication. We will explore four common implementation methods with code examples, examine their inherent pitfalls, and see how Abstract API overcomes these limitations.

How to Implement Email Validation in PHP

PHP offers several methods to validate email address formats. Each approach provides a different level of strictness and complexity, from simple built-in functions to comprehensive, RFC-compliant libraries.

PHP's Internal Parser with `filter_var()`

This method uses PHP’s built-in "filter_var()" function with the "FILTER_VALIDATE_EMAIL" filter. It leverages the same internal parser that PHP's engine uses to build outbound addresses. This process correctly rejects invalid formats like comments or unescaped quoted strings. The code first removes any extra whitespace from the input with the "trim()" function before the validation occurs.

$email = trim($input);
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    …continue…
}

IDN-Aware Validation with `idn_to_ascii`

This technique enhances "filter_var()" to support Internationalized Domain Names (IDNs), such as those with non-Latin characters. The process involves three steps. First, the email address splits into a local part and a domain part. Second, the "idn_to_ascii()" function converts the domain into its ASCII-compatible Punycode equivalent. This conversion is necessary because "filter_var()" alone does not support Unicode domains, a gap noted in community discussion. Finally, the parts reassemble and pass to "filter_var()" for validation. This method requires the "intl" PHP extension.

list($local, $domain) = explode('@', $email, 2);
$domainAscii = idn_to_ascii($domain, IDNA_DEFAULT, INTL_IDNA_VARIANT_UTS46);
$emailReassembled = $local . '@' . $domainAscii;
if (filter_var($emailReassembled, FILTER_VALIDATE_EMAIL)) {
    …continue…
}

Comprehensive Validation with Egulias/EmailValidator

For a more robust, RFC-compliant check, you can use the Egulias/EmailValidator library, which is installable via Composer. This component provides a thorough implementation of RFC 5321, 5322, 6531, and 6532 grammars, with full UTF-8 support. To perform a check, you instantiate the "EmailValidator" class and call its "isValid()" method with the email and a validation strategy, such as "RFCValidation". The library also offers other strategies, including "DNSCheckValidation" and "SpoofCheck", which can be chained together for multi-layered validation.

use Egulias\EmailValidator\EmailValidator;
use Egulias\EmailValidator\Validation\RFCValidation;

$validator = new EmailValidator();
if ($validator->isValid($email, new RFCValidation())) { … }

Format Check with DNS MX Lookup

This method adds a layer of verification by checking a domain's Mail Exchange (MX) records. After a successful syntax validation with a method like "filter_var()", the code extracts the domain from the email address. It then uses the "checkdnsrr()" function to query for MX records associated with that domain. A successful lookup confirms the domain is configured to receive email, which helps catch typos like "user@gmil.com" instead of "user@gmail.com". The check is efficient because the OS resolver caches the result.

list(, $domain) = explode('@', $email, 2);
if (checkdnsrr($domain, 'MX')) {
    …address is at least routable…
}

Challenges of Email Validation in PHP

While PHP provides several validation methods, they present significant challenges. These range from incomplete RFC compliance and limited character support to the inability to confirm an email address's actual deliverability.

• The filter_var() function fails to support complex but valid formats allowed by RFC 5322, like quoted local parts. This leads to false negatives for valid addresses and false positives for some malformed ones.
• PHP's built-in filter_var() function is ASCII-centric and rejects addresses with Unicode characters. Even with idn_to_ascii, the validation still fails if the local part of the email contains non-ASCII characters.
• A successful syntax check with filter_var() does not guarantee deliverability. The function approves addresses with non-existent or misspelled domains, which requires a separate DNS MX lookup with checkdnsrr() to catch.
• The filter_var() function contains hard-coded policy choices that cannot be easily modified. To extend or relax these rules, developers must wrap the function with custom logic for regex, IDN handling, and DNS checks.