укажи в заголовках utf. че-то типа такого
PHP код:
$subject = "Thank You for visiting $sitename";
$message = "Hi $name,\nThank you for your interest in $sitename!\nCheers, $sitename $siteaddress";
$headers = "From: $adminaddress\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-type: text/plain; charset=UTF-8\r\n";
mail ($email, $sumject, $message, $headers);