Forwarding can be sniffed.
Technically any form of forwarding service can intercept emails since the data is going though their network and then that of the target email address. So even without a inbox so to speak your data is being sent though the host.ir connection therefor can be sniffed and depending on what encryption has been used to send the email determines how easily the email can be read. If the email is sent though insecurely not using SSL then the email is completely readable since all they would have to do is monitor the forwarding service.
So to answer your question, it depends on how the email is being sent. But at the end of the day if your concerned about host.ir then you should not use them as a forwarding service at all.