<?php
$agir = $_REQUEST['agir'];
if ($agir == 'ok'){
$email = $_POST['email'];
if (ereg("^([0-9,a-z,A-Z,.,_,-]+)([@])([0-9,a-z,A-Z,_,-]+)([.])([a-z,A-Z]{2,3})([.][a-z,A-Z]{2,3})?$", $email)) { 
    print "certo\n"; 
} 
else { 
    print "errado\n"; 
}
}else{
echo"
<form method=POST>
<input type=hidden name=agir value=ok>
<input type=text name=email>
<input type=submit value=OK>
</form>";
}
?>