I have now had a chance to test this on our set-up and check it still works. It does. We are on Garden plan, don't know if that makes a difference.
As far as I can see, the two important points are to send it from an agent's regular email address, and in the Admin section, under "Support Channels" >> "Email" to enable the last option: "For forwarded emails, use original sender as requester". In that section we have enabled options 1, 3 and 4.
When these forwarded emails create new tickets we do have to edit the result, as we don't want "Fwd" in the title, and we also strip out the forwarding details in the body of the email to prevent the mail address being visible to the contact.
Yes..the forward emailaddress is an agent in Freshdesk and the sender is a contact in Freshdesk.
Is the email address from which you forward an email, the address of an agent as recorded in Freshdesk? If not, it will not work as the system does not know thisi is an agent.