Bulk email sending using sleep function

$between_delay = 10;
$send_delay = 1;

for ( $sent=0; $row = mysql_fetch_array($result); $sent++ ) {

if ( ($sent % $between_delay) == 0 )
  sleep( $send_delay );

$emailall = $row[0];
$message = stripslashes($message);
mail("$emailall", "$subject", "$message", "From: $email");
}