Labels are not sent as part of the forms posted data.
Labels are only used by the browser when displaying the form to the user.
In Universal Email you need to add the label informtion before the form output manually.
In the code for the email message, you have:
$MailBody = $MailBody . "<p>";
$MailBody = $MailBody . ((isset($_POST["PPqtySencillo"]))?$_POST["PPqtySencillo"]:"");
$MailBody = $MailBody . "</p>\r\n";
$MailBody = $MailBody . "<p>";
$MailBody = $MailBody . ((isset($_POST["CAqtySencillo"]))?$_POST["CAqtySencillo"]:"");
$MailBody = $MailBody . "</p>\r\n";
$MailBody = $MailBody . "<p>";
$MailBody = $MailBody . ((isset($_POST["CCqtySencillo"]))?$_POST["CCqtySencillo"]:"");
If you want something to be displayed before the Form element value, it needs to manually added, for example change
$MailBody = $MailBody . "<p>";
$MailBody = $MailBody . ((isset($_POST["PPqtySencillo"]))?$_POST["PPqtySencillo"]:"");
$MailBody = $MailBody . "</p>\r\n";
to:
$MailBody = $MailBody . "<p>Pechuga de Pollo";
$MailBody = $MailBody . ((isset($_POST["PPqtySencillo"]))?$_POST["PPqtySencillo"]:"");
$MailBody = $MailBody . "</p>\r\n";
the problem you are experiencing with the checkboxes is because you have not given them a checked value.
you have:
<input id="PPqtyMedDocena" name="PPqtyMedDocena" type="checkbox" value="" checked="checked"/>
the value attribute is what will be posted if the checkbox is checked.