email form: <label> tags instead of $key

[Paris]

I'm using form to email.
In the email sent, how could i get the <label></label> tags instead of
the input name?

So the email reads:
First name: John
Last name: Smith

instead of:
fn2: John
ln2: Smith

In the html form, usual label input pair :

<label for="fn2">First name</label>



I'm guessing in this:
$message .= $key." : ".$_POST[$key]."\n";

I want the label instead of the $key

I just don't know how...

Thanks

P.