The place where it goes is in app/code/core/Mage/Contacts/controllers/IndexController.php at line 100 in line. It looks like the reply address for the email messages is already set to the email address from the message, so if you just want easier answers, I would suggest not spoofing it.
Another problem you'll probably see is that sending email with a fake "from" address can cause your site to be quickly blacklisted by many email providers, which could affect the rest part of your business.
However, if you still want to do this, change this code slightly in this file:
$mailTemplate->setDesignConfig(array('area' => 'frontend')) ->setReplyTo($post['email']) ->sendTransactional( Mage::getStoreConfig(self::XML_PATH_EMAIL_TEMPLATE), Mage::getStoreConfig(self::XML_PATH_EMAIL_SENDER),
Hope this helps!
Thanks Joe
source share