SOMEONES not reading the tutorial carefully.
Nor the "README" file properly either
, because if you accurately read the $postmaster configs, the bit bolded in RED
$postmaster - The envelope sender address to use for all emails sent by the script. This address will recieve bounce messages if any of the emails cannot be delivered.
If in doubt, put your own email address here. , is what gives the definition of what that variable does. It's ONLY for "bounced" emails and has nothing to do with the "From:" header. The "email" value is what will change that "firstname.lastname@example.org" to the sender's email addy.