We have a mailcow server setup behind a NAT. On this same network, we have a Windows server running SmarterMail. When we would send from mailcow to SmarterMail, the mail header in the SmarterMail email would show our router’s private IP in the first “Received From”. We setup a transport map in mailcow admin UI using example.com (a SmarterMail domain) as the destination, with the SmarterMail server’s private IP address in Next hop. Now, the SmarterMail mail header shows “Received From” the mailcow server’s private IP. Problem is, it is still failing SPF because the mailcow server’s private IP is not in the SPF (as well as it shouldn’t be). I know we can setup a rule in SmarterMail to ignore spam checks coming from mailcow server’s private IP, but we were hoping there was another way around it.