In the file language.php the line
$language["mail_message_sent"]="Message sent through HuMo-gen (PHP) from the website.";
can be changed to
$language["mail_message_sent"]="Message sent through HuMo-gen (PHP) from the website by ".$_SERVER[REMOTE_ADDR]. " ".gethostbyaddr($_SERVER[REMOTE_ADDR]);
It won't work every time (ip detection has its quirks) but it may provide an extra clue if you get an incomplete, erroneous or puzzling email through the site form.
Cheers
Dani