Inspection of e-mail addresses based on the specification of the RFC2822 Addr-spec

RFC2822_AddrSpec.class.php

<?php
/**
 * e-mail address specification.
 *
 * http://blog.livedoor.jp/dankogai/archives/51189905.html
 *
 * RFC-2822 3.4.1 Addr-spec specification
 *      https://www.ietf.org/rfc/rfc2822.txt
 */
class RFC2822_AddrSpec {
    /**
     * check e-mail address
     */
    static function is_valid($addr) {
        $atom       = "[a-zA-Z0-9_!#\$\%&'*+\\/=?\^`{}~|\-]+";
        $dot_atom   = "$atom(?:\.$atom)*";
        $quoted     = '"(?:\\[^\r\n]|[^\\"])*"';
        $local      = "(?:$dot_atom|$quoted)";
        $domain_lit = "\[(?:\\\S|[\x21-\x5a\x5e-\x7e])*\]";
        $domain     = "(?:$dot_atom|$domain_lit)";
        $addr_spec  = $local.'@'.$domain;
        return preg_match('/^'.$addr_spec.'$/', $addr);
    }
}