Multiple Checkbox Values not showing
FULL FORM:

<form id='contactus' action='<?php echo $formproc->GetSelfScript(); ?>' method='post' enctype="multipart/form-data" accept-charset='UTF-8'>

<input type='hidden' name='submitted' id='submitted' value='1'/>
<input type='hidden' name='<?php echo $formproc->GetFormIDInputName(); ?>' value='<?php echo $formproc->GetFormIDInputValue(); ?>'/>
<input type='hidden'  class='spmhidip' name='<?php echo $formproc->GetSpamTrapInputName(); ?>' />


<fieldset >

<dl>
<dd>*Name (last, first)
<input type="text" name="name" size="33" value='<?php echo $formproc->SafeDisplay('name') ?>'>
  <span id='contactus_name_errorloc' class='error'></span>
</dd>
</dl>

<dl>
<dd>*Email Address <input type="text" name="email" size="35" value='<?php echo $formproc->SafeDisplay('email') ?>'>    <span id='contactus_email_errorloc' class='error'>    </span>
</dd></dl>

<dl>
<dd>*Construction Experience <input type="radio" name="construction_experience" id="construction_experience" value="Yes<?php echo $formproc->SafeDisplay('experience') ?>">Yes<input type="radio" name="construction_experience" id="construction_experience" value="No<?php echo $formproc->SafeDisplay('experience') ?>">No </dd></dl>

<dl>
<dd>*You must have valid drivers license, please select all that apply: <br />
<input type=checkbox name="valid_license[]" id="valid_licenseD" value="D<?php echo $formproc->SafeDisplay('valid_license') ?>">D license
<input type=checkbox name="valid_license[]" id="valid_licenseG" value="G<?php echo $formproc->SafeDisplay('valid_license') ?>">G license
<input type=checkbox name="valid_license[]" id="valid_licenseG2" value="G2<?php echo $formproc->SafeDisplay('valid_license') ?>">G2 license
</dd></dl>

<p><strong>Enter additional comments in the space provided below:</strong></p>

 <dl>
<dd> <span id='contactus_message_errorloc' class='error'></span><textarea name="message" id="message" cols="60" rows="8"><?php echo $formproc->SafeDisplay('message') ?></textarea></dd></dl>

<dl>
<dd>*Resume (insert attachment) <input type="file" name="resume" id="resume" value="" size="30">
<div><span class='error'><?php echo $formproc->GetErrorMessage(); ?></span></div>
   <span id='contactus_photo_errorloc' class='error'></span>
</dd></dl>

<p style="padding-left:60px;"><input type="submit" class="button primary" value="Submit Application" />   <input type="reset" class="button primary" value="Clear Form" name"clear" />

</fieldset>
</form>

require_once("class.phpmailer.php");

/*
Interface to Captcha handler
*/
class FG_CaptchaHandler
{
function Validate() { return false;}
function GetError(){ return '';}
}
/*
FGContactForm is a general purpose contact form class
It supports Captcha, HTML Emails, sending emails
conditionally, File atachments and more.
*/
class FGContactForm
{
var $receipients;
var $errors;
var $error_message;
var $name;
var $email;
var $message;
var $from_address;
var $form_random_key;
var $conditional_field;
var $arr_conditional_receipients;
var $fileupload_fields;
var $captcha_handler;

var $mailer;

function FGContactForm()
{
    $this->receipients = array();
    $this->errors = array();
    $this->form_random_key = 'HTgsjhartag';
    $this->conditional_field='';
    $this->arr_conditional_receipients=array();
    $this->fileupload_fields=array();

    $this->mailer = new PHPMailer();
    $this->mailer->CharSet = 'utf-8';
}

function EnableCaptcha($captcha_handler)
{
    $this->captcha_handler = $captcha_handler;
    session_start();
}

function AddRecipient($email,$name="")
{
    $this->mailer->AddAddress($email,$name);
}

function SetFromAddress($from)
{
    $this->from_address = $from;
}
function SetFormRandomKey($key)
{
    $this->form_random_key = $key;
}
function GetSpamTrapInputName()
{
    return 'sp'.md5('KHGdnbvsgst'.$this->GetKey());
}
function SafeDisplay($value_name)
{
    if(empty($_POST[$value_name]))
    {
        return'';
    }
    return htmlentities($_POST[$value_name]);
}
function GetFormIDInputName()
{
    $rand = md5('TygshRt'.$this->GetKey());

    $rand = substr($rand,0,20);
    return 'id'.$rand;
}


function GetFormIDInputValue()
{
    return md5('jhgahTsajhg'.$this->GetKey());
}

function SetConditionalField($field)
{
    $this->conditional_field = $field;
}
function AddConditionalReceipent($value,$email)
{
    $this->arr_conditional_receipients[$value] =  $email;
}

function AddFileUploadField($file_field_name,$accepted_types,$max_size)
{

    $this->fileupload_fields[] =
        array("name"=>$file_field_name,
        "file_types"=>$accepted_types,
        "maxsize"=>$max_size);
}

function ProcessForm()
{
    if(!isset($_POST['submitted']))
    {
       return false;
    }
    if(!$this->Validate())
    {
        $this->error_message = implode('<br/>',$this->errors);
        return false;
    }
    $this->CollectData();

    $ret = $this->SendFormSubmission();

    return $ret;
}

function RedirectToURL($url)
{
    header("Location: $url");
    exit;
}

function GetErrorMessage()
{
    return $this->error_message;
}
function GetSelfScript()
{
    return htmlentities($_SERVER['PHP_SELF']);
}

function GetName()
{
    return $this->name;
}
function GetEmail()
{
    return $this->email;
}
function GetMessage()
{
    return htmlentities($this->message,ENT_QUOTES,"UTF-8");
}

function SendFormSubmission()
{
    $this->CollectConditionalReceipients();

    $this->mailer->CharSet = 'utf-8';

    $this->mailer->Subject = "Online Application from $this->name";

    $this->mailer->From = $this->GetFromAddress();

    $this->mailer->FromName = "thermosealinsulation.ca";

    $this->mailer->AddReplyTo($this->email);

    $message = $this->ComposeFormtoEmail();

    $textMsg = trim(strip_tags(preg_replace('/<(head|title|style|script)[^>]*>.*?</\1>/s','',$message)));
    $this->mailer->AltBody = @html_entity_decode($textMsg,ENT_QUOTES,"UTF-8");
    $this->mailer->MsgHTML($message);

    $this->AttachFiles();

    if(!$this->mailer->Send())
    {
        $this->add_error("Failed sending email!");
        return false;
    }

    return true;
}

function CollectConditionalReceipients()
{
    if(count($this->arr_conditional_receipients)>0 &&
      !empty($this->conditional_field) &&
      !empty($_POST[$this->conditional_field]))
    {
        foreach($this->arr_conditional_receipients as $condn => $rec)
        {
            if(strcasecmp($condn,$_POST[$this->conditional_field])==0 &&
            !empty($rec))
            {
                $this->AddRecipient($rec);
            }
        }
    }
}

/*
Internal variables, that you donot want to appear in the email
Add those variables in this array.
*/
function IsInternalVariable($varname)
{
    $arr_interanl_vars = array('scaptcha',
                        'submitted',
                        $this->GetSpamTrapInputName(),
                        $this->GetFormIDInputName()
                        );
    if(in_array($varname,$arr_interanl_vars))
    {
        return true;
    }
    return false;
}

function FormSubmissionToMail()
{
$ret_str='';
foreach($_POST as $key=>$value)
{
    if(!$this->IsInternalVariable($key))
    {
        $value = htmlentities($value,ENT_QUOTES,"UTF-8");
        $value = nl2br($value);
        $key = ucfirst($key);

        // CHANGES BEGIN HERE.....
        // This loop looks over all the $_POST values. Need to isolate the `valid_licenses` and do something special with it.
        if ($key == "valid_license") {
           $value = implode(", ", $value);
           // Now $value will output as the comma-separated values list.
        }
        // CHANGES END HERE

        $ret_str .= "<div class='label'>$key :</div><div class='value'>$value </div>n";
    }

}
foreach($this->fileupload_fields as $upload_field)
{
    $field_name = $upload_field["name"];
    if(!$this->IsFileUploaded($field_name))
    {
        continue;
    }

    $filename = basename($_FILES[$field_name]['name']);

    $ret_str .= "";
}
return $ret_str;
}
function ExtraInfoToMail()
{
    $ret_str='';

    $ip = $_SERVER['REMOTE_ADDR'];
    $ret_str = "<div class='label'>IP address of the submitter:</div><div class='value'>$ip</div>n";

    return $ret_str;
}

function GetMailStyle()
{
    $retstr = "n<style>".
    "body,.label,.value { font-family:Arial,Verdana; } ".
    ".label {font-weight:bold; margin-top:5px; font-size:1.2em; color:#333;} ".
    ".value {margin-bottom:15px;font-size:1.2em;padding-left:20px;} ".
    "</style>n";

    return $retstr;
}
function GetHTMLHeaderPart()
{
     $retstr = '<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">'."n".
               '<html><head><title></title>'.
               '<meta http-equiv=Content-Type content="text/html; charset=utf-8">';
     $retstr .= $this->GetMailStyle();
     $retstr .= '</head><body>';
     return $retstr;
}
function GetHTMLFooterPart()
{
    $retstr ='</body></html>';
    return $retstr ;
}
 function ComposeFormtoEmail()
{
    $header = $this->GetHTMLHeaderPart();
$formsubmission = $this->FormSubmissionToMail();
$extra_info = $this->ExtraInfoToMail();
$footer = $this->GetHTMLFooterPart();

$message = $header."<div class='label'>Job Application Submission From thermosealinsulation.ca: </div><p>$formsubmission</p><hr/>$extra_info".$footer;

return $message;
}

function AttachFiles()
{
    foreach($this->fileupload_fields as $upld_field)
    {
        $field_name = $upld_field["name"];
        if(!$this->IsFileUploaded($field_name))
        {
            continue;
        }

        $filename =basename($_FILES[$field_name]['name']);

        $this->mailer->AddAttachment($_FILES[$field_name]["tmp_name"],$filename);
    }
}

function GetFromAddress()
{
    if(!empty($this->from_address))
    {
        return $this->from_address;
    }

    $host = $_SERVER['SERVER_NAME'];

    $from ="nobody@$host";
    return $from;
}

function Validate()
{
    $ret = true;
    //security validations
    if(empty($_POST[$this->GetFormIDInputName()]) ||
      $_POST[$this->GetFormIDInputName()] != $this->GetFormIDInputValue() )
    {
        //The proper error is not given intentionally
        $this->add_error("Automated submission prevention: case 1 failed");
        $ret = false;
    }

    //This is a hidden input field. Humans won't fill this field.
    if(!empty($_POST[$this->GetSpamTrapInputName()]) )
    {
        //The proper error is not given intentionally
        $this->add_error("Automated submission prevention: case 2 failed");
        $ret = false;
    }

    //name validations
    if(empty($_POST['name']))
    {
        $this->add_error("Please provide your name");
        $ret = false;
    }
    else
    if(strlen($_POST['name'])>50)
    {
        $this->add_error("Name is too big!");
        $ret = false;
    }

    //email validations
    if(empty($_POST['email']))
    {
        $this->add_error("Please provide your email address");
        $ret = false;
    }
    else
    if(strlen($_POST['email'])>50)
    {
        $this->add_error("Email address is too big!");
        $ret = false;
    }
    else
    if(!$this->validate_email($_POST['email']))
    {
        $this->add_error("Please provide a valid email address");
        $ret = false;
    }

    //message validaions
    if(strlen($_POST['message'])>2048)
    {
        $this->add_error("Message is too big!");
        $ret = false;
    }

    //captcha validaions
    if(isset($this->captcha_handler))
    {
        if(!$this->captcha_handler->Validate())
        {
            $this->add_error($this->captcha_handler->GetError());
            $ret = false;
        }
    }
    //file upload validations
    if(!empty($this->fileupload_fields))
    {
     if(!$this->ValidateFileUploads())
     {
        $ret = false;
     }
    }
    return $ret;
}

function ValidateFileType($field_name,$valid_filetypes)
{
    $ret=true;
    $info = pathinfo($_FILES[$field_name]['name']);
    $extn = $info['extension'];
    $extn = strtolower($extn);

    $arr_valid_filetypes= explode(',',$valid_filetypes);
    if(!in_array($extn,$arr_valid_filetypes))
    {
        $this->add_error("Valid file types are: $valid_filetypes");
        $ret=false;
    }
    return $ret;
}

function ValidateFileSize($field_name,$max_size)
{
    $size_of_uploaded_file =
            $_FILES[$field_name]["size"]/1024;//size in KBs
    if($size_of_uploaded_file > $max_size)
    {
        $this->add_error("The file is too big. File size should be less than $max_size KB");
        return false;
    }
    return true;
}

function IsFileUploaded($field_name)
{
    if(empty($_FILES[$field_name]['name']))
    {
        return false;
    }
    if(!is_uploaded_file($_FILES[$field_name]['tmp_name']))
    {
        return false;
    }
    return true;
}
function ValidateFileUploads()
{
    $ret=true;
    foreach($this->fileupload_fields as $upld_field)
    {
        $field_name = $upld_field["name"];

        $valid_filetypes = $upld_field["file_types"];

        if(!$this->IsFileUploaded($field_name))
        {
            continue;
        }

        if($_FILES[$field_name]["error"] != 0)
        {
            $this->add_error("Error in file upload; Error code:".$_FILES[$field_name]["error"]);
            $ret=false;
        }

        if(!empty($valid_filetypes) &&
         !$this->ValidateFileType($field_name,$valid_filetypes))
        {
            $ret=false;
        }

        if(!empty($upld_field["maxsize"]) &&
        $upld_field["maxsize"]>0)
        {
            if(!$this->ValidateFileSize($field_name,$upld_field["maxsize"]))
            {
                $ret=false;
            }
        }

    }
    return $ret;
}

function StripSlashes($str)
{
    if(get_magic_quotes_gpc())
    {
        $str = stripslashes($str);
    }
    return $str;
}
/*
Sanitize() function removes any potential threat from the
data submitted. Prevents email injections or any other hacker attempts.
if $remove_nl is true, newline chracters are removed from the input.
*/
function Sanitize($str,$remove_nl=true)
{
    $str = $this->StripSlashes($str);

    if($remove_nl)
    {
        $injections = array('/(n+)/i',
            '/(r+)/i',
            '/(t+)/i',
            '/(%0A+)/i',
            '/(%0D+)/i',
            '/(%08+)/i',
            '/(%09+)/i'
            );
        $str = preg_replace($injections,'',$str);
    }

    return $str;
}

/*Collects clean data from the $_POST array and keeps in internal variables.*/
function CollectData()
{
    $this->name = $this->Sanitize($_POST['name']);
    $this->email = $this->Sanitize($_POST['email']);
    $this->ConstructionExperience = $this->Sanitize($_POST['ConstructionExperience']);
    foreach ($_POST['valid_license'] as $license) {
// Append each sanitized element onto valid_license[]
    $this->valid_license[] = $this->Sanitize($license) ;
}

    /*newline is OK in the message.*/
    $this->message = $this->StripSlashes($_POST['message']);
}

function add_error($error)
{
    array_push($this->errors,$error);
}
function validate_email($email)
{
    return eregi("^[_.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+.)+[a-zA-Z]{2,6}$", $email);
}

function GetKey()
{
    return $this->form_random_key.$_SERVER['SERVER_NAME'].$_SERVER['REMOTE_ADDR'];
}

}

?>`

<input type=checkbox name="valid_license[]" id="valid_license" ... />

// Something like
foreach ($_POST['valid_license'] as $license) {
  // Append each sanitized element onto valid_license[]
  $this->valid_license[] = $this->Sanitize($license);
}

function ComposeFormtoEmail() {
  $header = $this->GetHTMLHeaderPart();
  $formsubmission = $this->FormSubmissionToMail();
  $extra_info = $this->ExtraInfoToMail();
  $footer = $this->GetHTMLFooterPart();

  // Assign this to a variable
  $licenses = implode(", ", $this->valid_license);

  // Then insert that variable into `$message`
  $message = $header."Job Application Submission From thermosealinsulation.ca :<p>$licenses</p><p>$formsubmission</p><hr/>$extra_info".$footer;
  //---------------------------------------------------------------------------^^^^^^^^^^^^^^^^

  return $message;
}

function FormSubmissionToMail()
{
    $ret_str='';
    foreach($_POST as $key=>$value)
    {
        if(!$this->IsInternalVariable($key))
        {
            // MOVED THIS BLOCK FROM BELOW...
            // CHANGES BEGIN HERE.....
            // This loop looks over all the $_POST values. Need to isolate the `valid_licenses` and do something special with it.
            if ($key == "valid_license") {
               $value = implode(", ", $value);
               // Now $value will output as the comma-separated values list.
            }
            // CHANGES END HERE

            $value = htmlentities($value,ENT_QUOTES,"UTF-8");
            $value = nl2br($value);
            $key = ucfirst($key);

            $ret_str .= "<div class='label'>$key :</div><div class='value'>$value </div>n";
        }

    }
    foreach($this->fileupload_fields as $upload_field)
    {
        $field_name = $upload_field["name"];
        if(!$this->IsFileUploaded($field_name))
        {
            continue;
        }

        $filename = basename($_FILES[$field_name]['name']);

        $ret_str .= "<div class='label'>File upload '$field_name' :</div><div class='value'>$filename </div>n";
    }
    return $ret_str;
}

### Now that this is the correct location, go back and remove the changes we made to `ComposeFormToEmail()`