if($in{'ChkboxName1'}){
$in{'form-to'} .= ',EmailGroup1@Domain.com';
}


if($in{'ChkboxName1'}){
$in{'form-to'} .= ',EmailGroup2@Domain.com';
}

if($in{'ChkboxName1'}){
$in{'form-to'} .= ',EmailGroup3@Domain.com';
}


$in{'form-to'} =~ s/^,//;