Email format validation in Php using regular expressions

if(isset($todo) and $todo=="test"){
if (!eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $email)){
echo "<center>Invalid email</center>";
}else{
echo "<center>Valid Email</center>";}
}