validate email

valid_email.php

<?php

class Valid
{
	/**
	 * Check an email address for correct format.
	 *
	 * @link  http://www.iamcal.com/publish/articles/php/parsing_email/
	 * @link  http://www.w3.org/Protocols/rfc822/
	 *
	 * @param   string   email address
	 * @param   boolean  strict RFC compatibility
	 *
	 * @return  boolean
	 */
	public static function email( $email, $strict = false )
	{
		if ( $strict === true ) {
			$qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]';
			$dtext = '[^\\x0d\\x5b-\\x5d\\x80-\\xff]';
			$atom  = '[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+';
			$pair  = '\\x5c[\\x00-\\x7f]';

			$domain_literal = "\\x5b($dtext|$pair)*\\x5d";
			$quoted_string  = "\\x22($qtext|$pair)*\\x22";
			$sub_domain     = "($atom|$domain_literal)";
			$word           = "($atom|$quoted_string)";
			$domain         = "$sub_domain(\\x2e$sub_domain)*";
			$local_part     = "$word(\\x2e$word)*";

			$expression = "/^$local_part\\x40$domain$/D";
		} else {
			$expression = '/^[-_a-z0-9\'+*$^&%=~!?{}]++(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d++)?$/iD';
		}

		return (bool) preg_match( $expression, (string) $email );
	}
}