This is form is used to illustrate two important concepts:
(1) using fieldname[] to allow multiple values to be chosen (in this case, send_to). View source code to see the brackets.
(2) using a checkboxes to hide the email address of the recipient and further prevent spam abuse. And... choose multiple recipients for the email. Note - You must change controls.php from
$set['dropdown_recipient'] = '0';
to
$set['dropdown_recipient'] = '1';
At approximately line 23
And you must put multiple recipients in controls.php
$set['recipient'] = array('you@youractualemailaccount.com', 'another@email.com');