/**
 * Verifies that an email is valid.
 *
 * Does not grok i18n domains. Not RFC compliant.
 *
 * @since 0.71
 *
 * @param string $email Email address to verify.
 * @param boolean $deprecated Deprecated.
 * @return string|bool Either false or the valid email address.
 */
function is_email( $email, $deprecated = false ) {
	if ( ! empty( $deprecated ) )
		_deprecated_argument( __FUNCTION__, '3.0' );

	// Test for the minimum length the email can be
	if ( strlen( $email ) < 3 ) {
		return apply_filters( 'is_email', false, $email, 'email_too_short' );
	}

	// Test for an @ character after the first position
	if ( strpos( $email, '@', 1 ) === false ) {
		return apply_filters( 'is_email', false, $email, 'email_no_at' );
	}

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

	// LOCAL PART
	// Test for invalid characters
	if ( !preg_match( '/^[a-zA-Z0-9!#$%&\'*+\/=?^_`{|}~\.-]+$/', $local ) ) {
		return apply_filters( 'is_email', false, $email, 'local_invalid_chars' );
	}

	// DOMAIN PART
	// Test for sequences of periods
	if ( preg_match( '/\.{2,}/', $domain ) ) {
		return apply_filters( 'is_email', false, $email, 'domain_period_sequence' );
	}

	// Test for leading and trailing periods and whitespace
	if ( trim( $domain, " \t\n\r\0\x0B." ) !== $domain ) {
		return apply_filters( 'is_email', false, $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 ) ) {
		return apply_filters( 'is_email', false, $email, 'domain_no_periods' );
	}

	// Loop through each sub
	foreach ( $subs as $sub ) {
		// Test for leading and trailing hyphens and whitespace
		if ( trim( $sub, " \t\n\r\0\x0B-" ) !== $sub ) {
			return apply_filters( 'is_email', false, $email, 'sub_hyphen_limits' );
		}

		// Test for invalid characters
		if ( !preg_match('/^[a-z0-9-]+$/i', $sub ) ) {
			return apply_filters( 'is_email', false, $email, 'sub_invalid_chars' );
		}
	}

	// Congratulations your email made it!
	return apply_filters( 'is_email', $email, $email, null );
}