Validar email PHP

validar_email

function VERIFICA_EMAIL($email){
    $email =  strtolower(trim($email));
    $mail_correcto = 0; 
    if ((strlen($email) >= 6) && (substr_count($email,"@") == 1) && (substr($email,0,1) != "@") && (substr($email,strlen($email)-1,1) != "@")){ 
       if ((!strstr($email,"'")) && (!strstr($email,"\"")) && (!strstr($email,"\\")) && (!strstr($email,"\$")) && (!strstr($email," "))) { 
          if (substr_count($email,".")>= 1){ 
             $term_dom = substr(strrchr ($email, '.'),1); 
             if (strlen($term_dom)>1 && strlen($term_dom)<5 && (!strstr($term_dom,"@")) ){ 
                $antes_dom = substr($email,0,strlen($email) - strlen($term_dom) - 1); 
                $caracter_ult = substr($antes_dom,strlen($antes_dom)-1,1); 
                if ($caracter_ult != "@" && $caracter_ult != "."){ 
                   return 1; 
                }
             }
          }
       }
    }
    return 0;
}