No need for jQuery. And it isn’t necessary to open a new window. Protocols which doesn’t return HTTP data to the browser (mailto:, irc://, magnet:, ftp:// (<- it depends how it is implemented, normally the browser has an FTP client built in)) can be queried in the same window without losing the current content. In your case:
function redirect()
{
window.location.href = "https://stackoverflow.com/questions/10172499/mailto:mail@example.org";
}
<body onload="javascript: redirect();">
Or just directly
<body onload="javascript: window.location.href="https://stackoverflow.com/questions/10172499/mailto:mail@example.org";">