[kontrabass]

Make a new plugin, with hook location "paidsub_build".

For the title, enter anything.

For the code, enter:

vbmail_start();
$useremail = "$user[email]";
$subsubject = "TalkBass Subscription Processed";
$adminmessage = "Dear $user[username], \n\nThank you for your donation! ETC ETC ETC ETC ETC ETC";
vbmail($useremail, $subsubject, $adminmessage);
vbmail_end();

This will send an email out to the user upon completion of their subscription processing.