What happens if you change:
$headers .= "From: ".$_POST["fieldFormName"]."<".$_POST["fieldFormus"].">\nReply-To: ".$_POST["fieldFormEmail"]."";
To
$headers .= "From: ".$_POST["fieldFormName"]."<".$_POST["fieldFormus"].">\nReply-To: ".$_POST["fieldFormEmail"]."\n";
Notice the \n at the end of the line.