sanitize_email() WordPress Function

function sanitize_email( $email ) {
	// Test for the minimum length the email can be.
	if ( strlen( $email ) < 6 ) {
		/**
		 * Filters a sanitized email address.
		 *
		 * This filter is evaluated under several contexts, including 'email_too_short',
		 * 'email_no_at', 'local_invalid_chars', 'domain_period_sequence', 'domain_period_limits',
		 * 'domain_no_periods', 'domain_no_valid_subs', or no context.
		 *
		 * @since 2.8.0
		 *
		 * @param string $sanitized_email The sanitized email address.
		 * @param string $email           The email address, as provided to sanitize_email().
		 * @param string|null $message    A message to pass to the user. null if email is sanitized.
		 */
		return apply_filters( 'sanitize_email', '', $email, 'email_too_short' );
	}

	// Test for an @ character after the first position.
	if ( strpos( $email, '@', 1 ) === false ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'email_no_at' );
	}

	// Split out the local and domain parts.
	list( $local, $domain ) = explode( '@', $email, 2 );

	// LOCAL PART
	// Test for invalid characters.
	$local = preg_replace( '/[^a-zA-Z0-9!#$%&\'*+\/=?^_`{|}~\.-]/', '', $local );
	if ( '' === $local ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'local_invalid_chars' );
	}

	// DOMAIN PART
	// Test for sequences of periods.
	$domain = preg_replace( '/\.{2,}/', '', $domain );
	if ( '' === $domain ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_period_sequence' );
	}

	// Test for leading and trailing periods and whitespace.
	$domain = trim( $domain, " \t\n\r\0\x0B." );
	if ( '' === $domain ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_period_limits' );
	}

	// Split the domain into subs.
	$subs = explode( '.', $domain );

	// Assume the domain will have at least two subs.
	if ( 2 > count( $subs ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_no_periods' );
	}

	// Create an array that will contain valid subs.
	$new_subs = array();

	// Loop through each sub.
	foreach ( $subs as $sub ) {
		// Test for leading and trailing hyphens.
		$sub = trim( $sub, " \t\n\r\0\x0B-" );

		// Test for invalid characters.
		$sub = preg_replace( '/[^a-z0-9-]+/i', '', $sub );

		// If there's anything left, add it to the valid subs.
		if ( '' !== $sub ) {
			$new_subs[] = $sub;
		}
	}

	// If there aren't 2 or more valid subs.
	if ( 2 > count( $new_subs ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_no_valid_subs' );
	}

	// Join valid subs into the new domain.
	$domain = implode( '.', $new_subs );

	// Put the email back together.
	$sanitized_email = $local . '@' . $domain;

	// Congratulations, your email made it!
	/** This filter is documented in wp-includes/formatting.php */
	return apply_filters( 'sanitize_email', $sanitized_email, $email, null );
}